OK, this is an area in which I have expertise. I've been doing Pet Therapy visitations for more than 10 years now. I visit at the Children's Hospital every other week and at a nursing home once a month. I have 3 cats and my oldest Lab in the program. The younger Lab still has to calm down some.
Although my Lab does have her CD, I do not think it is a necessity. As long as you have a calm, gentle dog I think you would be OK. But every Pet Therapy group has their own rules.
I really enjoy my visits, and have been rewarded richly by my experiences.
A funny story: I had taken my Chocolate Lab to the Children's and introduced her "this is my chocolate Lab, Bailey, she is (was then) 5 years old etc..." The first little boy I visit licks his fingers, touches her head, licks his fingers again and said "Mommy, she doesn't TASTE like chocolate!" How do you explain that to a 3 or 4 year old?