I can answer this since I'm the director of the album.
The main thing with this album is that since it's Mega Man, we wanted to get a bunch of remixers who were familiar with the material and able to deliver their work in a timely manner. I also personally looked at a bunch of artists I had good experiences working with before. Fortunately for us, OCR has been running fairly large Mega Man based compos for the past couple of years (like the Grand Robot Master Remix Battles and the Wily Castle Remix Gauntlets). This gave us a great big pool of artists to approach for the album; artists that knew and liked Mega Man music, and also were proven to be able to put together solid tracks in a short amount of time.
Larry and I then compiled a list of artists we thought would be a great fit, and then we divided the list into stages based on things like musical ability and availability, and then emailed and contacted our first stage of remixers to fill out the roster, then the second stage, and finally third stage. Once we exhausted that list (the list was fairly large but many artists declined, citing unavailability), I posted a thread in Recruit & Collaborate to fill out the rest.
I want to point out that many of the artists we approached came to our attention primarily because of the Mega Man compos, and I'm really glad to have a lot of fresh faces on the album. I also want to stress that–and I know Metal Man was joking but I want to say it anyway–this wasn't a case of "oh I'll just pick my friends to do this." Availability and efficiency were big factors here, and a lot of "big names" were approached later rather than sooner, because we had a good idea of their availability (or rather, lack thereof).