I don't imagine they would "see" 100% in infrared. Their eyes and the Pit organs are separate but I would imagine it's a combination of senses working at the same time. My pickiest eater seemed to be way more interested in a F/T mouse if I perked both of it's ear up before offering it to her. So I definitely think they pickup on the silhouette of their pray which could also be a reason that ASF rats trigger a better response with their more pronounced ears...

Then again, I could be reading into things too much.