Regarding using x-root-window settings, it might work, but I have a feeling it probably won't due to the setup of the device (compositor, etc). Is the source for hildon desktop open? Someone could always add it themselves.
Animated gif just became a still image locked at the first frame as background, pretty much what I expected, and the flash format isn't even supported of course.
Then I dunno if there are any hacks to make things work differently.