I've seen this done ONCE humanely. A couple I know put an add in the local paper for people who already owned Betta's to use them in their wedding, and believe it or not enough people had Betta's that they got their wish, and then they all went back home to loving families after the wedding was over.
I'd say if you couldn't garruntee that the Betta's got to go home to people who would take care of it then you have NO
business using them for a wedding.
I liittle of topic, I went to the local Walmart last night at midnight, and all but one of their betta's where dead on the shelf, out of like 30, SO SAD!!!!