I don't think so. One in awhile I get a few pieces of junk mail that will slip through the GMail junk filter and Mail will annotate them as "junk". But there is no way that I can see to have a junk mail count and folder even if I set one up in Mail. Anyway, I wouldn't want one because of the large amount of junk that GMail filters out.
Sometimes I find genuine mail gets put in the GMail junk folder but I have to access my account on line at the GMail server in order to read it.