PM / VM at least a mod or higher and ask them if the site is ok. Usually if you link to other "rival" sites or one of those money-making referral sites, well, you'll get a ban. If it's just something like Voidfront or one of those "give me internets" or "help my X grow" it should be ok. And I think links to blogs / portfolios / DA should be ok too, as long as they don't encourage users to leave MPGH.
But make sure you ask a mod or higher first.