It's going to depend on the facts and circumstances.  If there was an existing mortgage which was comprised of home acquisition debt that was rolled into the reverse mortgage at inception then part of the interest paid will still be based on refinanced home acquisition debt and be deductible.  You just have to dig through the history and find out what happened.

I haven't seen enough of these to know which is more common.  I suspect you're right and the vast majority of the interest will be non-deductible home equity interest but you just have to start turning over stones and see what you find.

Rick