Google will index cloaked websites until it's reported as cloaked or they work it out for themselves. As soon as that happens the site will be penalised and will drop from the search results. I wouldn't recommend cloaking at all generally, unless you're using it on a throwaway site and just want to generate some quick revenue or traffic, and don't really care if it fails completely.
I always wondered that as well, because cloaked websites don't have any content so it wouldn't make any sense for them to get listed.