A few things that he might enjoy...
The stingray lagoon experience should be very blind-friendly. You wade into a shallow lagoon and form a large circle with the other people in the group. Then you stand still and they hand out some food for the rays, who, knowing what's coming, swim very close and let you feel their amazing velvety bodies! I think that would be awesome if he's not creeped out by the idea of rays slinking around... because you stand still and they come to you, and because it's a touch experience.
The aviary. If you join one of the staff members working in there, they will chat with you and introduce you to the friendliest birds, who will perch on your arm or your head while you feed them. (I wouldn't try grabbing the birds in there WITHOUT one of the staff members helping, but I'm pretty sure they would know which birds would like to be petted and would supervise)
The dolphin experience... I think it would be worthwhile because of the touching and riding. Also the staff member supervising gives an informative, entertaining talk about your dolphin.
I think you should call and ask them if they can make any suggestions or accommodations! Here's a paragraph from their General Park Information page at discoverycove.com. It's mostly about mobility issues but it suggests they are willing to work with disability issues:
Guests with Disabilities
Discovery Cove can accommodate guests with disabilities
who are able to maneuver themselves with limited
assistance (or with the aid of a personal assistant) during
their dolphin experience and in the various wading
locations. Discovery Cove also offers specially-designed
outdoor wheelchairs with oversized tires for easy
maneuvering on the beach. The wheelchairs are not
self-maneuverable and guests will need assistance operating them.
Wheelchairs can be reserved by calling 1-877-557-7404.
