Board Thread:Support Requests - Community Management/@comment-26335203-20150831142129/@comment-3026053-20150831143140

You can basically do whatever you want on a wiki as long as it doesn't violate Wikia's Terms of Use and that wiki's local policy, and this wouldn't do that, so it's allowed.

That said, however, banned users already bear a tag that they're block in their masthead. As such, placing an additional template on their profile seems redundant and even a bit mean as it is putting even more emphasis on the fact that said user is blocked. For infinitely blocked users, that's "fine", since they won't be able to come back, but for temporarily blocked users, that may widen the rift between them and the community and create unnecessary drama.