Some of Ambuscade's Snare cards have wording along the lines of "Put this card next to the Hero Character Card with the fewest HP". A player in our group (whose Hero was incapacitated) argued that his Hero Character Card had "the fewest HP". I (thinking like a programmer) argued that there was difference between "0" and "NULL". Opinions?
If you are incapped you don't have HP so it should go to a hero that is not incapped.
Powerhound is correct.
An incap side of a Character card has no HP number on it, is not a target and does not have HP. Zero is a number you can have, but your incap side lacks the ability to have HP, even 0 hp.
There's an exception to that. One incap power on Huge Skyscraper is all about being a 1hp target while incapped.