You will have to get the permission of each venue for each Gig, if you want to be on the safe side.
Yes, water based hazers can and do set off smoke detectors. There is no difference between water based and oil based as far as an optical sensor knows. That said, it really depends on how much haze you pump out and that is directly dependent on the airflow in the room. If it's cold outside and the facility has an older thermostat only HVAC system then you may not have much airflow allowing the haze to spread throughout the room somewhat evenly with not much volume from the haze machine. If you have in a newly renovated facility with CO2 detection it will either burp or strongly flush outside air into the room periodically purging all haze meaning you need to keep the machine on longer at a higher setting providing uneven haze coverage with more possibility of a sensor triggering.
You DO NOT need a person from the fire department to stand fire watch. Any person can do it, you just have to designate the person and will need someone standing fire watch the entire time the system is disabled.
Yes it will... may take a little bit longer, but it will. The smoke detectors now-a-days are so accurate, that the smallest particulate in the air will send the fire department to your gig. Only way around it is to play in a room that IS NOT equipped with detectors, or you have to have a fire department member standing by (at cost) to turn off the system and watch for fire danger. That's why you see so many foggers and hazers for sale now. Everyone is getting away from using them.
You DO NOT need a person from the fire department to stand fire watch. Any person can do it, you just have to designate the person and will need someone standing fire watch the entire time the system is disabled.
I have delt with this multiple times and not just for DJ events. My family owns an environmental company in the DC area and have delt with this on job sites many times and not just for a few hours down time but for weeks even. You will be required to notify the local fire department & or the monitoring company for the system. The real question is it worth the effort. For a very large event with a fairly involved lighting setup I could see it as something worth the hassle. For a smaller gig I would either offload the entire responsibility on the Site & Client or not offer it at all.