I'm not inclined to put too much math here because I don't want to get it yanked, but I would think that in most cases the zerker will be doing more damage with percent-based armor rather than pt-based because its all about damage per second rather than armor-punching. The effect will probably be far more advantageous to non-high-damage mod zerkers than high-damage mod zerkers, but without really looking at the numbers I'd still think that all zerkers would benefit. I haven't played a zerker character, so I'm not really sure about the delay for a multiple-swing attack.

The big difference is that "damage per swing" becomes fairly meaningless, as compared to "damage per second."