The GUU has always been a private members club- its in its statutes. The difference now might be that they actually enforce it, although with their perilous financial situation and the likelihood it'll hit their takings, don't expect it to last.
As for the question, since Unions are slightly different (i.e. not usually open to Joe Public) they'll be able to get round the new laws. It stops things like happy hours and BOGOFS (not that you ever see the latter), but doesn't stop a regular promotion like £1 drinks Sun-Wed (which Viper does) or anything like that.