Hi Katelyn,
> I'm working on creating a dashboard with a layer that has points/locations derived from a csv.
Yes, you should make it a hosted feature layer in either ArcGIS Online or Portal for ArcGIS, so Ops Dashboard can work with it.
> When attempting to load the layer into the dashboard, the layer (and others) are grayed out with a message "Layer Not Accessible".
Have you ensured that the feature layer(s) have been shared correctly? Are you the owner of all the layers in the web map that you're trying to create a Dashboard for?
Hope this helps,