I don't have a whole lot of experience with giants, but the giant warriors I did have the dex based skills failed a LOT more often. Often to the point that I was pissed I even bothered to take them.

Evade for a giant will be much the same I imagine, since it fires rather sporadically as it is. Being as it's dex based I doubt it would fire often enough to make a difference in PK when you could spend those pracs on something more worthwhile.