I don't know whether to thank you for alerting me to a new BBQ specialty or blame you for adding another stop on my already ridiculously overbooked schedule. (Just kidding--I always love adding new dishes to my BBQ must-try bucket list. Keep 'em coming.)
I just got off the phone with both branches of Bennett's and here's what I was told. Imagine a whole pork shoulder: the top is the Boston butt; the bottom is the shoulder ham (sometimes called the picnic ham). As you know, the latter has a piece of shank (leg) attached, which gives it a triangular shape. That piece is your hog leg.
If you want to read about a related cut (but prepared in a completely different manner), check out the Schweinhaxen (spit-roasted ham hocks--a Munich specialty) describe in Planet Barbecue on page 245.
As for me, guess I'll be heading to Pigeon Forge or Gatlinburg, TN, pretty soon.