I have done it before and it has worked, but I was wondering if it was acceptable to que for a random as a frost tank? I know frost is a dps tree and blood is a tanking tree so please don't point that out.

I wouldn't try tanking in frost spec for a random because that's about as dumb as healing on a mage. Frost WAS a tank spec but now it's dps. You could probably get away with it more at lower levels but at 85, you'd get booted easily. Just go blood and make frost your os.