I was wondering the same thing myself. Unless there is some sort of battery or alternate power source this type of heater might not be all that great of a fail safe. I'm sure at this day in age something like this must exist though. I guess if the unit did not have the ability to kick on in the event of a power outage you could always turn the gas on and light it manually...but if your not home to do this...
I'd go with low duty (computer type) UPS units for individual racks as well as one for an oil filled room heater. I guess if I had to only pick the rack or the space heater to be on a UPS I'd pick the space heater to keep the ambient temps steady.