The WHATWG doesn't really "exist" in quite the same way that the W3C does. There isn't Process for obtaining an opinion that you can then ascribe to an organisation rather than one or more individuals. It only represents the browser makers insofar as the specs hosted at whatwg.org accurately reflect what browsers implement. Sometimes this is achived by adjusting the browsers to match the specs; oftentimes the opposite occurs.

It is certainly the case that several individuals editing specs under the WHATWG banner have set out their opposition to DRM. It seems unlikely that Hixie will include it the HTML spec he edits unless, of course, we end up with something implemented in browsers that is both interoperable and open. Since "open" rather defeats the point of DRM, it's difficult to imagine that happening, however.