If you mean that you want the new Recorded TV folder streamed to the Xbox 360 as an extender directly by WHS, then I don't believe it's possible. The folders that the built-in streaming software can manage are set by Microsoft.
However, if you're just using the Xbox to read files from the shares, I think it should work as long as the format is one that the Xbox can play natively.
I'm not on the WHS team, I just post a lot. :)