10-4 The E mags and the Gen 3 Pmags (which share the exterior dimensions of the Emag) are supposed to be GTG for the HK.
Aftermarket AR mag compatibility can be a little hit or miss. Gen 1 Pmags run fine in my personal an work issued Colts but had fit / locking issues in my LMT and S&W. Conversely, Gen 1 ARC mags ran great in the S&W but wouldn't run at all in my Colts.