This driver, which competes alongside xf86-video-via and xf86-video-openchrome, now offers XvMC VLD support. However, it's not a traditional implementation of X-Video Motion Compensation, but rather Luc ended up designing his own X extension in the X protocol for sending MPEG slices to the hardware. This was done due to not liking the design of traditional XvMC implementations, which he describes in this blog post.
In the xf86-video-unichrome repository is this XvMC addition for the VT3122 and VT3108 ASICs with MPEG2 slice decoding support. XvMC is also supported by the OpenChrome driver.