Quick question.
Hey, so if at vet 3 s unit's damage was to be increased by 20%, does it mean that all weapons that the unit uses will have this bonus?
Yes.
Also, if a vet 3 squad was to reman a support weapon, does the crew still keep the vet 3 bonus?
If you reman an MG with vet 3 KCH then yes, the mg will still be manned by vet 3 KCH guys. However, the MG itself is not vet 3.