1) As far as I know, I'm using the latest version of both mods. PPA version 1.4 gold hotfix and the MMM 6.2 update posted in the MMM thread.
2) The problem appears to be a group of Outcasts fighting a group of raiders around 2-3 cells east of Agatha's house (so, Block 0,0, Sub-block 0,1, (3, 8) or (4,8), I think). With just PPA, there's no problem. With just MMM, there's no problem and there are more of each (6-7 Outcasts and raiders instead of the 3 without MMM). With both, it crashes every time.
I haven't run into this problem with any other group of power-armored enemies, including the outcast Outcasts (so to speak) in the raider faction or the Enclave. I also haven't run into it with other groups of Outcasts, though this is the first time I can remember I've seen an Outcast group so large (there are 6-7 of them and a robot with MMM installed) other than the group I had to fight for the Anchorage DLC, which gave me no problems. PPA does add tokens to powered-armored characters' inventories to distribute the PPA upgrades, and it's possible that this is causing a conflict. What I can't figure out is why it's localized to this specific group of Outcasts.