"White-label" is a term used to indicate a third-party solution/service being used and branded by another company, making it look like their own. Revenue Cycle Explorer (RCE) is another example. The underlying platform is owned/supported by a third-party. Marketo brands it as a feature that's part of the overall platform (as an add-on). Which is one of the downsides - in that Marketo has to rely on the third-party to continuously enhance/evolve the product. And in the case of RCE, it's been pretty much stagnant.
Also note that, with Marketo's Email Delivery Power Pack there is a limit to how many emails you can run through it every month. I think the cost goes up with additional emails, so you may want to ask your account manager for that break down and make sure it meets your needs. But we used it at a previous company and liked it. It was fairly easy to use once you have it all set up (set up was easy too!).