I'm sure Matt or some other more knowledgeable Rhino user will pitch in with a better theory/explanation, but here's mine for what it's worth.

When the Rhino is shot from a loop, the loop sort of wraps around the peg so to speak keeping the peg in one place. When you shoot a standard caliper style release directly off the string, it may slide up or down a little during the draw but because of the closed jaws it isn't going to come off the string. I can't see the peg of the Rhino staying put as it slides up or down the string.

The new & improved Rhino has more of a hook shaped peg, so maybe it wouldn't be a problem. But if you decide to try it I'd plan on wearing a helmet or at least a mouthpiece.

Another thought....there's also the issue of torque. If you should torgue the head of the release a little while shooting off of a loop, the loop will flex & move with the release. But torque the head a little while shooting off the string and the peg will surely slip off.