See
ADA National Network | Information, Guidance and Training on the Americans with Disabilities Act
I looked at the amendments act of 2008
From there. Definition of a service animal
Any dog that is individually trained to do work or perform tasks for the benefit of a person with a disability
Excluded: the crime deterrent effect of an animals presence and the provision of emotional support,well being,comfort,or companionship do not constitute work or tasks.
By that definition emotional support dogs are not covered under that act.
Interesting.