Calculating Probability with a Wild Card

[JoeU]

There is a home game in my area that uses a "wild card" in the game. The people who play the game state that a 5 of a kind now ranks ahead of a straight flush or royal flush. Is this mathematically correct? You could technically have a full house become a 5 of a kind, but this hand, by no stretch of the imagination, beats a straight flush. In this instance, there are 8 cards in the deck that make a 5 of a kind, and 9 cards that make a straight flush. But on the other hand, in a normal game, there are 5 cards that make a straight flush, but only 4 cards that make quads. I'm not a math wizard, so I was hoping that someone here could answer these questions.

Thanks
Joe