We never even see what type of marriage ceremonies they have in FFVII. Though no matter the ceremonial dress required, he would feel inclined to have a left shoulder pad. I guess that if anyone ever tries to give him a right shoulder pad as well he will be kicking and screaming.
To me it would seem more logical if he had the shoulder pad on the right side. I mean, when he swings a sword he tends to expose his right shoulder more than the left. Would he not want to protect his right side more than the left because it is a closer target?
(Tennyo, I think you infected me with that over-thinking sickness
)