OS should affect all the damage you do so it should work with OS. Crit rate not sure though. The thing I'm not sure about yet is the combo. You kinda need that buff that replaced Stone Skin because the CS atm seems kinda meh. And it has a channeling time of 1 second, you are going to be so vulnarable to net bind's and vacuums etc (if they are still there Idk). Because you are going to channel the skill probably, then pop OS, then Rush, then CS.
Atleast when I was playing guard, and also in pservers I had to be careful not to get vacuumed as soon as I poped OS. And sometimes I even got perm-vacuumed. It's no fun lol.
But haven't looked into it enough yet. Only got to like level 10 to see what the leveling is like.
Not sure about the OP-ness though. You lose elemental damage which in this server should work against most classes since I don't think there will be too many +all stats. And in return you get a 35% chance of doing a double attack. It can be OP though if you get lucky and you hit a few AOE double attacks, if that **** works that is.