I just added vengeance 2 today, I previously had ven 15. my new total is 17 and it does add t the atk rating(no my str had nothing to do with it, it is always maxed. so there is no 15 cap on vengeance items, just the 250 max worn atk
There is no direct cap on vengance, instead there is a cap on worn +atk items. The most atk you can have from items is 250 raw (that is, before applying the melee bonus). Note, however, that avatar from primal weapons (and probably from the elemental BPs as well) DOES count towards this cap. For rogues that means that if you're proccing primal then swapping in RB you're left with 110 item +atk that you can get. That would be vengance 22. I do think that it is fair that the cap on vengance is so much higher than FT, as more FT makes a player much more effective than the same amount of vengance "points".