I have a Vega 56 here running with the new beta, I'm planning to release it as soon as I fix some outstanding issues with EDID emulation.
There's a serious limitation however with regards to the dotclocks these cards can support through HDMI. The minimum seems to be around 18 MHz, which not only prevents using low resolutions but even the usual 4:3 desktop modes like 640x480i. Super resolutions work nicely though, so they're perfectly usable for GroovyMAME.