Hey Jason, i have been testing with this functionality for quite a time now. The only way to create or mutate a record in a related table in ArcGIS online, is by using Collector for ArcGIS or ArcGIS pro. ArcMAP has the disadvantage making a replica of your data first before you can edit it and hope your sync will go right.
If you want to visualize you records in a map you even have to simplify you data in a new feature layer.
e.g. I have a asset with multiple recordings of problems that have to be solved. I want to show the mechanic a map with all the assets that have a specific problem.
So i join the asset features with the info from the relation table and make a new layer. Now the mechanic can select a specific problem of his choice, show were he has to go and solve the problem.
If anyone has a different solution i be very interested.
Best regards,
Richard Jansen