I pulled a 2 man tube from my 33 Express using one of the stern cleats. Didn't have any problems at all, but I was a bit careful (esp at first) that the tube wasn't going to swamp getting going. If the tube swamps, it puts tremendous pressure on the line and could possibly have damaged the cleat mounting, or even worse, ripped the cleat out which then becomes a high speed projectile aimed right at the occupants of the tube!
Anyways the angle of the line to the cleat made it hard / impossible for the tube to swamp so it all worked great. Towing wise - it was awesome... nice huge wake to bounce the riders through and all the folks on the boat had a great view of the kids... The fact that the tube wasn't centered was not a problem, and the boat handled as if the tube wasn't there.