http://meta.wikimedia.org/wiki/Talk:Hotel_Wikipedia#Is_this_a_copyright_viol... Essentially it's a parody of a copyrighted song, and thus fair use. If this were on one of the Wikipedias, it would not be allowed, since it's not in article space. Does this also apply to Meta?
Legally, it's almost certainly ok. What is allowed on Meta is only a subset of what is allowed by law, however, so I don't know if there are any Meta policies which forbid it.