A friend brought by a couple of mags that I'd not handled before, today. I learned a fair bit in the process.
The current DPMS mag has a narrower, but with a larger standoff, rear rib, than the current Armalite mag.
The current DPMS mag is also more square than the current Armalite mag, and is of very similar overall dimensions to a G3 mag.
I believe the mag catch height to be compatible.
I believe that the DPMS bolt catch would work in an Armalite lower; I'm not sure about the other way around.
Bottom line: You can't put an Armalite mag into a DPMS lower because the rib is too wide at the back, and I believe the main mag is also a little too long.
You can't put a DPMS mag in an Armalite lower because it's too wide throughout, particularly at the front, because the Armalite lower is cut for the tapered Armalite mag.
I still believe that you *could* cut an Armalite style lower to accept DPMS/SR25 mags. However, today's attempts at interchange suggest that an attempt at a jack of all (AKA a magwell opened up to allow for either to work) would probably be proverbially master of none, and would have to have the mag-locating features opened up so loose that both mags would slop around and probably have trouble.
On the assumption that DPMS mags are entirely compatible with SR25's, I would assume that the same would be true of the SR25 mags. Unfortunately for me, I don't know anybody who actually has one of those.