Scott's clients include pet owners who want to mate their pets and don't want "illegitimate relations" in their home. Others want companionship for their pets, and some pet owners just want a public ceremony to emphasize how esteemed their pets are.
As crazy as I am about my dogs (we do celebrate their birthdays), I am not about to hold a doggie wedding.
Loki and Thor are adopted brother and sister, after all, and letting them marry would be yucky. :P
(Seriously, I would NEVER go there. Their relationship is 100 percent sibling and 0 percent romantic. They just don't have that kind of chemistry. Plus they're both fixed. And mostly, Loki thinks Thor is an extremely annoying little brother.)