I don't know about their Jacobson's organ but I believe my Boas can see really well.
They watch me intently every I go near the fridge where their supper is stored and get all excited, hoping we'll have an impromptu 'extra' feeding day.
I've also seen videos of Boas grabbing birds out of the air and I don't think heat sensing would be terribly efficient for that.
I did find this interesting page
http://www.eyedesignbook.com/ch3/eyech3-f.html
And this:
Communication and Perception
Like most snakes, boa constrictors rely on strong vomeronasal senses. Their tongues flick continuously, bringing odor molecules into contact with the chemosensory (vomeronasal) organ in the top of their mouths. In this manner, they constantly sense chemical cues in their enviornment. Boa constrictors have good vision, even into the ultraviolet spectrum. In addition, they can detect both vibrations in the ground and sound vibrations through the air through their jaw bones. They do not have external ears. Unlike most boids, boa constrictors lack thermosensory pits. (Mattison, 2007; O'Shea, 2007; Sillman, et al., 2001; Stone and Holtzman, 1996)
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