Put the organizer in a bind, I'm sure! I'm all for giving the handicapped opportunities for culture, but a special arrangement should probably have been made for the group you mention, and for others (such as young children) who can't reasonably be expected to keep quiet for long.
When the event is 100% based upon enjoying sound this should not be tolerated regardless of age or IQ. 10 years ago, when I took my daughter to these concerts and she would start to act up I removed her from the theater and took her to the lobby until she shut up.
The artists for these concerts don't make the mega-bucks like the normal screech and dance trash and usually just get paid enough for expenses plus a little. Many of the artists are my friends and I know most are paid under $1,000/concert.