Freesync works, G Sync too, you have to set it in the Nvidia control panel. However, only from the NVIDIA GTX series, from the GTX 1060 6Gb.
I have the GTX 1080, everything runs without problems. Freesync must of course be activated in the screen.
I'll test it a bit more, but so far I have a very good impression of the monitor. It has a great price-performance ratio.

The same model is available as a non-curved model called asus vg27aq.
It even has official confirmation from Nvidia that it is G sync compatible. This asus vg27wq screen has exactly the same technical specifications. That's why I ordered it here today, because the same question came up for me. So I'm pretty sure it's G sync compatible.

Salute Nico

Basically, only Freesync is officially supported.
I'll check tonight whether G-Sync can be activated on the monitors.

Greetings. Tim