yea they do work but at a HUGE disadvantage, it is HIGHLY recomended to have a
crew of that same nation for every line, i.e. UK sailors for UK ships, and US sailors for
US ships

the only exception though is that the US medic works on UK ships at 100%, so im
told. and same for IJN and KM(which ever one has the medic) and for france
apparently any one will do.

Supports will, but with a large performance hit. You'll most likely be best off leveling
engineers/repairers of that nation.