Will be installing a SmartThings gateway, but am a bit concerned if multiple gatways (for other purposes) can co-exist? Case in point is I also have a Honeywell Redlink gateway to the HVAC system operating on 908.42 MHz.
As long as they’re far enough apart that the signal has had time to spread, it’s usually OK. It’s very similar to having two or three Wi-Fi networks in the same building. I’m running three z wave hubs now in one 1500 square foot house, but they’re in different rooms.
And there’s usually no problem if neighbors in an apartment building each have a Z wave hub.
At minimum I try to put mine about 10 feet apart. Z wave antennas are usually Omni directional (360°), but as I mentioned the signal doesn’t spread for a few feet so you can get noise interference if they’re right next to each other.