The Ground Traffic option in the Addon Manager controls only some animated cars/vehicles that moves around in FSDT airports.
There are not many of them and they won't be loaded if the airport is not loaded (which is usually from 10 to 15 NM out, depending on the scenery), so they won't take much memory (exactly zero, outside the airport range) and, even if they are loaded, their impact is negligible so, if you are getting OOMs, they won't be fixed by this.
Don't waste your time disabling these things, and especially anything related to our airports, which are very aggressively optimized to save VAS. If you are so close to memory exhaustion, your first areas of optimization should be (listing in order from the most impacting ones):
- The memory-hungry airplane you are probably using
- The scenery visual range (don't set it to Large)
- The AI Traffic Density
- The Autogen Density
- If you use FSX, try to enable DX10, which will save quite a bit of RAM, or use FSX:Steam Edition, which is better optimized.