I think you can block anyone you want to block. But it is limited to 200 users.
Thus, this blocking does not appear to be a violation of any guidelines. It is allowed.
If you do not like the questions they are posting, then just ignore those questions. That would be the easiest solution.
There are plenty of other questions to answer, although you may need to check out other sections of Y/A. (Since the R & S section is nearly dead.)
By the way, reporting anything these days seems to be a waste of time. I've seen people report my answers, and I just ignore it. Nothing ever happens. I don't think there is any moderation of Y/A, at least none that I have seen.
I wish Y/A would get rid of the mask feature. I would like to see who is behind the mask.