I would be wary just sticking a UTH on without a thermostat. Usually UTH's have a range of temps that they hit when they are plugged in without being regulated. If you haven't tested the pad running for 24hrs with a thermometer than can log your max/min temps its very risky not having a thermostat.

I would never recommend not having a thermostat on your heating elements, even a dial rheostat you can buy at HD for 10 bucks is better than nothing at all.