Different backends can be used with whatsup via the --module option, but I don't think there's a way to list what modules are available. That would be convenient.
Also, it appears that if you specify a bad module, it will fallthrough to an available one?
>whatsup --module=foobar
up: 319: catalyst[1-172,174-187,189-202,204-241,243-313,315-324]
down: 4: catalyst[173,203,242,314]