Was playing ROM 2.61 on a Gigantic Map with Raging Barbarians, and had this problem:
I'm considerably ahead tech-wise, and had just (within a turn or two) discovered Gunpowder. On the border of another nation (Carthage) a decent stack (5-6) of Musketmen appear. Power 17 Musketmen. I'm the only one with Gunpowder and don't even have Matchlocks yet, so barbarians should not be spawning Musketmen. Whatever is spawning the barbarians is apparently basing it off the vanilla unit tech requirements and not the mod's, since Gunpowder alone will allow Musketmen on vanilla, but not even Arquebusiers on ROM.