I'm going to preface my opinion with the fact that I never trade those etf's directly. I only trade their options... but. If my broker was unable to make shares available to short on the most liquid stocks EVER I would kick them to the curb.
It's *close* to the same thing... except that it's 2x leverage (something you hinted at) and, as those who have been trading these funds on a regular basis will tell you, they don't correlate 100%.