I'm not certain of the details of the A330 RAT. But most of these have governors controlling variable pitch props to maintain a uniform speed (or at least prevent overspeed). In the event that the RAT is a constant pitch (variable speed) unit, its speed would also be a function of its electrical and hydraulic loads at any moment. And oil temperature/viscosity.
I doubt a manufacturer would bother to determine the necessary performance curves to make this of any use for such a low probability event.
As others have stated, GPS can provide a ground speed that, with some performance curves can be used to limp along in the event of a pitot static system failure.
