I asked again on FFmpeg mailing list for access to VDPAU decoded frames.
Answer from email@example.com:
Tue, 23 Jun 2009 13:47:06 +0200
> You can do it as of today since the actual decoding in on the caller
> Call VDPAU getDataSurface at the end to retrieve the YV12 data
> Hoping that helps
I will keep you informed in this thread of possible VDPAU support.