How should damage counters be put on a Pokémon?
Primeape from Plasma Freeze has this ability, Karate Chop, however the ability doesn't care if you consolidate counters into something else like higher value counters or dice, counters as referred to by this are the standard 10 damage counter. Changing to some other method to show the 50 damage on the primeape does not change the effect of the ability, effectively the ability does 80-[the total damage Primape has taken].

Generally though I would suggest using Dice to mark damage, it's a lot simpler to have 2d6 on the card than it is to cover it with 8 counters (as the 9th would knock it out) This is however an opinion there, and temper it with how things are enforced where you play and by your opponents.