Religion would work against Perry with moderates and independents in the general. All the Dems have to do is trot out Sun Goddess guy or some of Perry’s anti-Baal activist buddies.
Otoh, religion will work for Romney. Assholes like Bill Maher and a cast of thousands will just not be able to restrain themselves from attacking his Mormonism. The GOP spin machine will have no trouble generalizing this into a bigoted assault by the opposition and tarring the Democrats with it. They would try the same thing in defense of Perry, of course, but it would be an impossible sell.