Yes, it is.
Adaptive Sync is the base generic term, then FreeSync and G-sync are built around that. HDMI VRR is a transmission standard developed by HDMI consortium to standardize Adaptive Sync over HDMI. Display port's version of Adaptive Sync over HDMI basically.
DP to monitor was opened up to Hdmi to monitor by both AMD and Nvidia but not on the HDMI VRR standard.
So a Freesync HMDI is not compatible with HDMI VRR. this is what AMD promised in Dec 2018 and haven't seen anything since.
NVidia recently released their HDMI port to do HDMI VRR, a version of DP G-Sync compatible capability now over HDMI. Freesync over HDMI doesn't work with G-sync monitors as yet. LG B/C/E 9 series being the first G-sync over HDMI compatible monitors around.
So we're getting close. RX 5700 series cards need to support HDMI VRR and we'll come full circle.