1 - I have produced factory workers, in the hope they could boost a bit my assembly machines, but oddly, they are not listed in the allowed modules for them, which is strange. You would think that assembly machines in Factorio is what is closest to a factory!
2 - Even stranger is that assembly machines will accept all types of military personnel. Or that a lab accepts a factory worker!
3 - I see that the refinery accepts it, except when I try to add them to it, it does not work. I know how to add personnel properly, as I can add a laborer to an assembly machine.
So it's all weird... People that should go in some places don't or can't, while others like heavy machinegunner could ...