[2022] Does % fire pene works for my hammerdin?

You don’t be get increased damage from spell lightning damage for the hammers themselves. That could add damage to a triggered ability like Smite. The hammers are not spells. It requires to have the spell tag to be affected by any spell scaling and I don’t think hammers can get a spell tag.

Edit: also just to reference the initial question, resistance penetration isn’t damage.