No, last tiem i checked if there knocked out there skills dont apply till they get 10 or 25% health back or something.

If the companion was present at the beginning of a battle, they will still provide party skills during that battle, the same applies to the player (for example, if you provide surgery and get knocked unconsious, you will still provide that skill untill the end of the battle). Companions won't provide party skills if they were in the "red" (below 15 hp) threshold at the beginning of a battle.