I think it's silly to say that heat from below is "foreign" to snakes and other basking animals. Many, many different reptiles will bask on a rock or roadside AFTER the sun has gone down that is still radiating heat after sitting in the sun all day.

That being said...If you can use a single heat source to get the proper gradient in your enclosure, I don't see a problem with that. I've seen plenty enough evidence of snakes thriving on nothing but an overhead source of heat. The critical thing is to make sure that proper temps are maintained consistently...not whether that heat comes from above or below.

That's my opinion on the matter, anyhow.