Hulu has responded with a lovely mail regarding use of the service on PlayStation Plus.
Turns out, you will not be required to be a PS+ member to subscribe to the service, just during the evaluation period.
Here's the mail in full:
With the launch of Hulu Plus there have been many rumors started and we are trying our best to remedy the situation. Specifically to your question, the Playstation Plus service is only a requirement during the preview period.
Once the preview period ends you should be able to download the Hulu Plus app but that will still require the Hulu Plus subscription.
Right now we are limiting the number of users but Hulu Plus will be launching to the public very soon so stay tuned!
Good news, then.
Glad that's cleared up then.
Still no date, but Sony told us last week it would be announced soon.
Xbox 360 users get the service in "early 2011".