What if the umpire's a woman; is a ponytail okay?
And here are two partners (and I have had both):
A) Clean-cut guy and physically fit. He gets out of the car with badly wrinkled, non-uniform light gray pants; faded, sweat-stained purple mesh cap, canvas belt and faded navy t-shirt. He's wearing mostly black running shoes and black and gold and white pattern socks. He goes to his trunk and pulls out a balled-up, faded navy shirt with no association patch and says, "We're going navy, right?" and pulls it on. He was finished. I thought he went to the trunk to get started. (I was standing there in my charcoal slacks and black t-shirt after having called for black on black with charcoal the night before.)
B) Very overweight guy with a large moustache and one of those Frank Zappa things under his lip, and a ponytail that he eventually tucked up under his cap. He walked to the back of his car and opened it up and it looked like a men's store with a whole rack of shirts, slacks and jackets, and stacked up drawers and bins---all perfectly organized. He pulled on a clean, pressed Honig's uniform (right down to the poly-wools); a clean, creased, new-looking cap; a pair of shiny, all-black Reeboks. He was impeccable.
I would rather go onto a field with an impeccably dressed 280-pound version of Frank Zappa than a careless, slovenly, but well-groomed and physically fit version of Ray Liotta.
So appearance is important, but the uniform is drastically more important than the grooming or fitness of the man wearing it.