Is the loyalty cascade effect intentional? Either way, will definitely try this out.
Edit: Just lost my fort to them. First off I made the now obvious mistake of embarking with more Plump Helmet men than Dwarves (5 males, 10 females, one of each wartrained. I just copied my usual setup for dogs). I didn't realize the implications of what I had done at first, and calmly started mining some exposed nickel. Everything was going well for almost all of spring and I had a pretty decent mine going, as well as the beginnings of some above-ground structures. Eventually, 5 of my 7 Dwarves went into the mine to haul the garnierite out and the Plump Helmet men rebelled almost simultaneously, I assume it's because there were a lot more of them than dwarves around the wagon. They quickly formed a swarm and started chasing my Dwarves. The planter hid in one of the buildings on the surface and the expedition leader ran for the hills, but the rest were trapped in the mines.
It was a horror story from there. They ran down, cornered, and swarmed the engraver and the woodcutter in the upper floor, leaving only the two miners and the carpenter. The woodcutter did a number on one or two of them, but nothing too serious, only some shallow gashes and bruises. I had more hope for the miners, and drafted them to see if they could stop the Plump Helmet Men while the carpenter escaped to the deeper reaches of the mine. The miners were no slouches, but they only killed one or two, there were just too many. The carpenter didn't last much longer than they did. I abandoned shortly after.
You've done some good work here, sir. I haven't had such good ‼FUN‼ from within since my first encounter with Masterwork's bloodbeasts.