I’m pretty sure that’s correct. There was a period of about 80 years ( about 420-340 BCE, give or take a few years on either end), where the Persian empire lost control of Egypt and the Mendes dynasty ruled. The Persians reconquered it a few years before Alexander went rampaging east. Alexander then became pharaoh, and then the whole successor thing erupted when he died. Cue Ptolemy and his increasingly inbred descendants.
Greek/Carian mercenaries would have been in the Egyptian armies in the Saite and Mendes dynasties, and could easily have been part of garrisons under the Persians.
Speaking of garrison, I don’t know how active they were in field campaigns, but another interesting unit to model in Saite -Persian occupation - (maybe Mendes Egyptian armies would be the Jewish mercenaries at Elephantine. They were there to secure the Nile against incursions from the south and seem to have been taken into service with each regime that controlled Egypt. I haven’t read anything about how they were equipped, though. Researching that could turn into a rabbit hole… Herodotus doesn’t mention them, but they were definitely there during his tour. I don’t think that necessarily means Herodotus didn’t visit Elephantine in person; it could also be that the Jewish troops were equipped pretty much the same as other ‘native’ soldiers and didn’t stand out as unusual (they had already been there a long time at that point). That’s not as fun to model as a wargame unit though.