If running games full screen on the g-sync monitor it should work fine.
If using Nvidia surround to stretch the game on two screens, I guess the g-sync monitor refresh rate could still match the frame rate but this could look strange between the two monitors.
As long as the card has proper dual outputs and your not just splitting the cable for a cloned display (You're not doing this, nobody has done this for years) it should be fine. I'm not sure about G-Sync though, I believe you can have a G-Sync as your main display and a non g-sycn as secondary but never had one myself so might be worth googling a bit
I'd like to use g sync monitor as the main display and the other for shit stuff. Typical situation would be playing LoL on the G-Sync monitor, and having the other screen on Spotify or facebook.