I would agree with your opponent since template weapons already have rules that ignore range during overwatch. There is no location in the codex that I can recall where it states that the weapons must be in range, however the appropriate section of the BRB says:
BRB pg. 45 wrote:An Overwatch attack is resolved like a normal shooting attack (albeit one resolved in the enemy's assault phase) and uses all the normal rules for range, line of sight cover saves and so on.
So the only thing left would be whether the pathfinders count as being where the strike team is or where they currently are. I've always played this part as if the unit was at its current location, so if their out of range their out of range.
So I would say that your Pathfinders couldn't fire their pulse carbines, but they could fire their markerlights