I'd be interested in knowing that myself. Although I guess I could get off my a** and check it myself, since I have both.
OK, I did exactly that and went and checked. I did NOT mount it, but holding it up to the back-plate, I'm about 90% certain that it would. It looked like the bottom of the HEST sheath would line up with the bottom of the snap-strap that is used on the back-plate to attach that plate to PALS straps.
Ok, I'm ordering a back and pouch now, will post pics when it's all together! Thanks!