I'm not surprised about the mixed brands working, but I am surprised about the hot-swap working smoothly. Either you were lucky, phase-wise, when randomly connecting the generators, or they work a lot better than I expected. If you threw a Honda eu-series generator into the mix I'd expect the load balancing to not work as nicely because of the Hondas having a higher output voltage than the others.
I still remember all the posts about the generators going up in smoke if you connected different brands and/or connected one of the AC output lines to the case ground (i.e. the "2 leg" output theory).
