>>339497337
Yeah it's perfectly possible and has been done plenty of times. No additional setup is required at all. The vive/index light houses are external reference points and that synchronisation is just those two light houses pulsing in time by shooting a laser at each other to calibrate. The actual headset doesn't care how many other headsets or tracked devices are in the area so long as it can see the light houses.
I haven't properly tested it but I'm pretty sure they're just IR light because I managed to get my controller to track when it could only see the fire my fireplace. You could probably do that old wii trick where you replaced the light bar with a line of candles but I wouldn't be blindfolding and muffling my ears and swinging around in a room with open flames.