Giving a compatibility report on 7D + Sigma EF500 DG Super flashguns is probably a waste of bandwidth given the ages of the respective units, particularly the flashes. But, having acquired a 7D, and on the off-chance that someone might benefit, I might as well close this short thread with an update.
I can report that Sigma EF500 DG Supers work flawlessly in all wireless slave modes, including E-TTL II, to the built-in flash commander of the 7D I recently acquired. Unfortunately, I can also confirm that this particular Sigma model does not work at all in the 7D's hot shoe. In fact, I have established that the EF500 DG Super does not work on-camera with anything later than the 5DII and 50D (and only the later E-TTL II version of the flash, as I have, will work on those two bodies).
I have a Yongnuo 468 II on the way for 7D hot shoe duties.