I think it probably depends on the style - boxing I'd say no.

Judo yes - there's a guy in my Judo club who's completely blind and he competes often successfully against opponents with no disabilities.

I think the people he trains with have to be more careful than ayone else because he doesn't always know where the edge of the mats it.

I saw him throw a guy onto the floor over the edge of the mat once and the guy who was thrown got up very slowly!

The coaches do a lot of one on one work with him with a radio nearby so he has a point of reference and his dog sits beside the mats with everyone's bags quietly and so well behaved I nearly stepped on it once and it didn't react!

I guess it's ok in Judo because after you get the initial grip you can pretty much feel where your opponent is and more importantly where they are putting their weight.