Are suspended users able to edit their profiles, or are they prohibited from doing so?
Yes and no. I just tested it with my sock puppet. I suspended it 'for science', and now it gets a 404 when trying to open the 'Edit profile and settings' tab on that site (this has been reported as a bug here):
However, it's possible to edit another profile on the network and have its changes apply everywhere, thereby bypassing this restriction. (This deleted answer which I discovered later, after @Martin linked to the question, mentions it as well.) So this could be considered another bug, though it's not particularly harmful.