Yes you need ch skills 1100 to use a gsp but if you have the skillpoints available i highly recommand it because a gsp can easily tank defiler missions for you. I've done it myself.
GSPs can't be trusted. They sometimes stop attacking their current target and they run too much. Maulers run too and that's why I don't use them. TMBs or GSHs or rancors never run, that's why I always use my TMB or GSH for missions
I tried to do a kamurith defiler mission with my full grown gnarled rancor (Muffin ) and ended up losing a ton of stims. Rancors and gurrecks should have a better resistance against kinetic... They are after all the highest level pets in the game.