Yeah, signed up on the PC and got Saving Silverman then got an email about the $4.99 credit and it showed up when I activated the app on the 360. Here's part of the email as it extends past the 360.
SPECIAL OFFER: Activate VUDU on your Xbox 360®, Playstation® 3, Internet connected Blu-Ray™ players or HDTVs, and you're eligible to receive free* VUDU credits instantly. Use your credits and watch the latest HD new releases on us!