Can we blacklist this tag from getting a tag wiki?
I think a better solution would be to lock the tag wiki for untagged to something that explains what it is and what users should do when they see it (I have no idea how this will be implemented on the backend, but this is obviously the best solution to the problem). Something along the lines of:
These poor questions have lost all of their tags. Please help by retagging them.
All tags older than six months with only one questions get automatically pruned. A question that loses all its tags to this process gets the untagged tag. Please retag such questions accordingly.
Probably not the best possible description of untagged, but it'll do for a start I guess?