Is it possible to use Syncthing on a share/dataset that is set up to use AD permissions? I've played around with it a little, but everything I've read seems to indicate that Syncthing has to have its own user permissions.
There are two permissions that you can use. user permissions - give syncthing full access here. Thereafter, you can use the group permissions with active directory. Create an AD group and then give it the permissions you want.