I'm fishing really clear water and was wondering if I can use straight  10 pound braid for wacky rig?

Of course you can. There is no reason you couldn't. I never fish wacky rigs, I fish them T rigged, but 10lb straight braid is my everyday set up on all my spinning rods. All the water is all I fish is clear.

If you're fishing really clear water I would suggest a 6-8 pound fluorocarbon leader about 6' in length. Don't be afraid of line to line knots. I stubbornly stayed with straight fluorocarbon because I didn't want to learn how to tie the double uni knot. But I'm so glad I learned.

Try straight braid.  If you think you notice a decrease in bites, add a leader.

I've gone back and forth with straight braid on finesse gear especially wacky. Right now my spinning rod is 10lb power pro slick 8 and I feel my casting distance has improved after removing my leader. 

I use 15lb straight braid for mine, even in clear water. 15lb braid is so thin that I don't feel the fish can see it very well, and I have no problem catching them without a leader so I don't worry about it.