I know he voices a couple Imperial guards but does he voice any marriable ncps?
I've been trying to find a list of the characters that are done by him but I can't seem to find any.

no one has ever come across any gideon emery voiced npcs besides a few random guards? :'o

Unfortunately I haven't, sadly. Unless he wasn't using one of his trademark voices, in which case I could have simply not recognized him. Then again I haven't met all the marriageable male NPCs, so he might have voiced one for all I know.