I think I'm about to become a crazy oncidium alliance lady... because that is just gorgeous and now I want one!
I don't think their water requirements change much when they're in bloom, but I do think they are not as forgiving of you forgetting to water them when they are in bloom. When mine are not in bloom, I can get another day or two on watering, by spritzing the top of the medium with water, then giving it a good soak later.
When they were in bloom though, if I forgot to water them, I lost flowers so, just stay on your regular watering schedule and you should be good to go.