According to ChatGPT:
Yes - the Samsung Odyssey G9 (G95C) monitor does support NVIDIA G-Sync technology (or, more accurately, "G-Sync Compatible"). Here are the concrete details, and also some precautions to take.

✅ What's confirmed

According to the product sheet from a Swiss retailer (Galaxus): "Sync-Technology: AMD FreeSync Premium Pro, NVIDIA G-Sync".
Galaxus

A specialist website states that the monitor supports variable refresh rate (VRR) up to 240 Hz for "FreeSync / G-Sync Compatible".
Display Ninja

On the Samsung US website, for a slightly different model ("G95SC"), the information sheet states "G-Sync Compatible".
Samsung uk
+1

⚠️ A few nuances and conditions

"G-Sync Compatible" means that the monitor does not necessarily have NVIDIA's "certified" G-Sync hardware module (like some displays with a dedicated chip), but that it is validated to work with G-Sync via VRR. This may lead to differences in operation or compatibility.

An NVIDIA forum thread reports that for this "G95C" model, G-Sync mode does not work at 240Hz via HDMI, but only via DisplayPort at 240Hz. Via HDMI, it would only work up to 120 Hz.
NVIDIA

Other feedback (DisplayNinja site) suggests that activating VRR (FreeSync or G-Sync Compatible) can cause flicker in some applications, indicating that performance can vary depending on settings and content.
Display Ninja

🎮 My practical advice

If you're thinking of using this monitor with a VRR-compatible NVIDIA card (PC) or console :

Use DisplayPort 1.4 rather than HDMI if you want to take advantage of 240Hz and G-Sync Compatible.

In the NVIDIA control panel, enable "G-Sync Compatible" for this monitor.

In the monitor's OSD menu, make sure that "Adaptive Sync" or "VRR/FreeSync" is enabled.

Check in game that the frame rate varies within the supported range and that you have no undesirable effects (flicker, latency, etc).

If you're using HDMI and you're only doing 120 Hz, keep this limitation in mind.