I just got this rifle.  I have one mag that came with it and two that I bought on gunbroker.  My question is, are the mags DPMS specific or can I use M1A (or other) mags in it?

LR20 Pmags work.  I have most of the sizes of them.  You will need AR type mags.

Gen 2?  If so, I tried PMAGS and there was an issue, so I moved to the IDI 20 rounders and they work like a champ.

I use PMAGS.

I've had zero issues with either the Magpul or the IMI magazines.  The latter seem to be under-appreciated; they function smooth as butter, but I rarely hear anyone mention them.

I don't know if it is a Gen II.  The box just calls it an Oracle.

Has anyone had issues with the PMAG LR25 double feeding?  I've got a PWS MK2 and have only had a chance to try one of my four 25 rounders and it would double feed every 5-10 rounds but the 20 rounders I've used have all ran fine.

M14 mags, or FAL, will not work to answer your specific question. You need to stick with SR-25 pattern mags for the LR-308.  The old Armalite AR-10 mags will not work either but I think Armalite has changed their mags now to pattern after the SR mags, but do NOT quote me on that and certainly do not buy AR-10mags without checking first.  I do not follow Armalite so I don't know where I picked up that information and it could well be MIS-information.  

 I have used Brownells, DPMS, CP, and Mag-Pul in mine.  Of the four, I like the DPMS mags best.  Three of my 4 LR rifles are wildcats and the Brownells, CP, and Mag-Pul mags will not work, they swell too much or are difficult to tweak.  The DPMS mags are easily tweaked, hold the tweaking, and function flawlessly.  In my one standard caliber LR, the Brownells mags still tend to swell so I don't get that at all.  I got them when they first came out and they didn't work in anything I had so they are in the junk box now.  I have not tried any more so I don't know if they are better now or not.  The CP, MP, and DPMS work just fine in it, a .338 Federal.

Armalite has two different types of lowers the A models that use the original styled mags (modified M14) and the B models which use the SR25 pattern mags

308 pmags or Lancer L7

I was looking thru threads for feedback on these "IMI DEFENSE .308/7.62X51 20rd Polymer DPMS Pattern Magazine" and this seems to be all that I can find. Hasn't anyone else used these mags and provide more input?

I think it's the other way around.... The "A" uses the SR-25/original AR-10/P-Mag type and the "B" uses the modified M-14 mags.