Yes! You'll just use the feature(s) from the SDE db and load them into either a Map Viewer in your Enterprise Portal first (which is how I normally make my Field Maps regardless if I am using AGOL hosted feature layers or layers direct from the SDE simply because I'm 99% of the time going to use that map in Map Viewer as a template for other maps, apps, or dashboards. Once you have everything in that Map Viewer set the way you want (and make sure that in the Settings tab you have the box checked for use with Field Maps and the SDE layers set with the correct parameters for offline edits), then open up the Field Maps Designer direct from your Map Viewer from the upper right where you have quick access to the other apps (the 9 small squares icon next to the bell icon) and then from there set the additional parameters that will need to be set in Field Maps like the size of the offline extents and scale etc.
It is basically the same workflow as using a hosted feature layer directly from AGOL, it's just coming from a different source (your SDE db). Ensure that the users have the correct privs on those SDE features that are in the Field Map application so they can do what they need to do. Field Maps can get pretty robust with its functionality, so my recommendation, if this is your first iteration, is to keep it simple and give yourself plenty of time to get it set right and have either yourself and/or the crews test out a basic demo iteration with one or two editable features from the SDE db well ahead of time before production data collection begins so you can fix anything that you might have missed, or that the crews will want in the production product that might not have been left out in the demo iteration. There will be many different settings that you will have to become familiar with, but once you do, then you are set. Make sure you document in a dedicated Word document that you create just for Field Maps for each setting that you set and why you chose to set it that way. Once you get comfortable with it, then you can start adding additional functionality to it. Just don't go big on the first go, because it is likely going to not work right, and if you are creating offline areas with multiple features that are going to be edited, it can easily turn into a frustrating experience. Esri hasn't officially come out and said it (per an Esri tech support person who mentioned it to me), but each offline area you should kept below 500mb for performance reasons. And remember, you can only have 15 offline areas per Field Map.
So if you are working in a very large geographical extent, you WILL need to make multiple Field Maps to cover the entire territory your crews are working in. The same goes for the number of layers you add to the map. The first year we had only 3 layers and were able to grab HUGE offline areas that downloaded no problem. The next year the boss wanted 12 layers, and then I went to having to make a map with 15 offline areas for each county if the county was small enough. Some needed more than one Field Map. So, keep layers out of the map unless you really need them.
When the production field data collection is done, don't delete the Field Maps, just turn them to 'hidden' mode so that only the admin can see them. Then when you are ready to collect the same data in that same location just turn them back to viewable so your workers can use them again with hardly any extra effort on your part unless of course you need to add or remove some of the layers.
In the end, the biggest takeaway is to start out small and ensure you know what each option available in Field Maps Designer is for, and choose the right setting for each of them, and document the setting you chose as you set each parameter so you don't forget them. Then during initial testing, if something isn't working right, you can go back to your document, and make a correction to one parameter at a time to troubleshoot until you got it nailed down. Then add the other layers in you need and have the crews test each layer to ensure that everything is working correctly BEFORE production data collection begins.
Also, if you don't have a versioned environment set up for the layers you will be using, make sure that the crews are given their own specific offline territories to work in, which will keep you from having to worry about one person overwriting someone else's edits on any given day. If they inadvertently make incorrect edits to a feature that someone else had already made the correct edits for then you'd have to send someone out and gather the data again, and that would require a robust QAQC process in place to ensure that wasn't happening, so give specific people specific areas that they are allowed to work in to remove some of those concerns.
If you don't need the use of forms, but just need the editors to add or delete features, or to put data into specific fields, you could forgo the forms option in Field Maps designer and just use coded-value domains straight from the layers when you work with them in Pro. Up to you and the end-users how you want the end product from a UX/UI perspective.
As for using tracking being added to Field Maps, be cautious about using that. If a field crew person who has Field Maps on her iPhone or Android leaves the app on at the end of the day, it's going to show by way of the GPS on her phone, exactly which part of the house her bedroom is in, or where she goes after work. That's just one security concern out of many that you should be aware of. I saw that happen on the first day I turned on that feature during our first season with Field Maps, and I haven't used it since for obvious reasons.
Hope that gives you some ideas to speed up the onboarding of using the app. Sorry for any typos or grammar issues. Don't have the time to proofread atm.
