Rick Santorum is very clearly a heretic to the Catholic Church on evolution. There is no One True Fallacy there. The Vatican declares it to be true and is against creationism. I don't know any Catholics who behave like Santorum and as a layman Santorum has no real authority on the matter within the Church, whereas in a Baptist setting someone like Santorum could become a preacher expressing these views.
It also doesn't change the fact that he's a harmless ole prude.
To be fair, I think Santorum has always been coy about evolution. Like during the 2012 debates, he gave some idiotic, "If he [Huntsman] wants to believe we evolved from monkeys, he can" response. Not a wise response but also not a flat out denial. Pretty much a political answer given the audience at the time without giving his own belief.
Of course, if Rick doesn't believe in evolution and suggests that the Church rejects it, he's obviously wrong. But what TJ says above this post is also true.