This is what I do, but I run them off of a thermostat. I honestly just run all my enclosures, racks, and tanks on thermostats so I don't worry about burning the house down if I leave for the weekend or such.
With a dimmer you have to monitor the temp because as the ambient temperature fluctuates the tank temperature might as well. The thermostat will keep checking the tank temp and make the adjustments for you. There are some good inexpensive thermostats out there like this one:
All my geckos are housed in aquariums or storage tubs each uth on a dimmer. I periodically check them temps, to make sure they are correct. Is there a way to hook 6mats into one thermostat? I'd go broke having to buy 6 individual thermostats. I have also found when using a Repti-Temp thermostat that two uth that are same size in the same size glass tanks with same substrate can't be controlled by one thermostat. They both ran at different temps.
The only reliable way to have multiple cages on one thermostat is using heat tape or to make sure that all of the UTH are the same size and wattage. If you are checking the temps there shouldn't be a problem with the dimmer. I use racks so the thermostat option is just way easier and not expensive.