So currently, the way the heal active check works makes it impossible for the attacker of Bigfoot to be considered unable to provide heal exp when healed unless that guy is literally never attacking bigfoot.
The only issue would be the priest being marked as an 'inactive healer' which will require a bit more testing to verify the cause of this in a scenario of a bigfoot fight, and the best solutions. I assume the biggest issue is the attacker just doesn't take damage often enough.