I see it as seeing to this degree.
If the whole process is picked up and formatted by the brain exactly like it is for eyesight, then it is in all reality just as eyesight would be. That is what is being shown as a strong possibility in the Crotalinae. I do not see why this cannot be at all possible. It still may be a 6th sense thing as well. But, if properly formatted by the brain, it can be "seen" just as much as what is processed by the eyes. Seeing, in all respects, does not necessarily have to come from eye organs either. It is just that many forms of life has evolved to use these given organs to gain this sense. Yet, there are other methods of sight that the animal kingdom uses. So saying that something does not use eyes to "see" does not make it lacking in sight as we perceive it. We simply use a different organ of choice.
Still, there is a lot of detail and study left in this whole subject of heat sensing in snakes, along with sight. There is an interesting thread on heat pits at the VenomDoc forums if others would like to see more discussion of this subject.