[PeeWee]

Ayup, from what I've read, you could. Just make sure your rogue is proficient with the weapon or else he would get a -3 penalty for using it(core).

There are some pretty nice blunt weapons out there as I'm seeing while in chapter two. Would only try using them for that " cool effect" though. Try having a fighter not being proficient for something like a club and then use it offhand when ya dont have points for two weapon style. Talk about a BIG penalty. -2 for weapon and -8 for offhanding it.

Oh and if you couldn't backstab with anything else it may mean you are sufferinng from the -3 penalty from not having a proficiency point in that weapon skill as said above. You add that in with the "randomness" of the backstab going off and it would seem that you couldn't. Cloaking up and being behind the enemy never hurts but it still doesn't guarantee anything.