Seems like just about any nautical style brightly colored outfits would do the trick... we are visiting Nemo's world in Submarines, right? So the people that drive the subs should be...ya know...submarine style dressed people... I meant that to sound as choppy as it came out...just so you know...
Wouldn't they wear the old subs costumes? I thought the premise of the ride was to start out as the regular old sub ride and then Something Goes Horribly Wrong and the sub is suddenly in NemoLand. If so, it would make sense for the cast members to dress as sub operators.
They used to wear blue short-sleeved shirts, jeans, a white web belt, a nautical hat, and blue Keds-type tennies.
Back in the golden days, it was all guys working on the subs. I assume there will now be gals working the ride, but they could wear the same costume as the guys. (I'm not sure if gals were working subs right before they closed; that was after my time.)
My wife claims to have seen them. It was a blue shirt (possibly Hawaiian) with a logo for Nemo on the t-shirt. Also remember that while I can't confirm this the Nemo for the attraction is intended as an acryonm for some type of oceanographic research, and the story is about exploring an underwater volcano anyway.