AngryGoldfish
Old N Gold
Not all of the Freesync monitors use HDMI for it, some of them require the use of Displayport. For instance, the one I'm using right now will only use Freesync via Displayport - AOC G2460PF.
Oh, well, OK. But the technology does support transfer through HDMI. I can't remember what mine is. I just use DP. To be honest, using Gsync via DP only is not a huge drawback.