Its not going to be a safety risk if dew runs down the tube onto it, is it?
If not, I would suspect the biggest problem may be it's too warm and may cause thermal currents in your OTA which will give you mushy shots...
A dew heater ona newt mirror seems to be contrary to my understanding of what most imagers with newts are trying to do. What you need is a little hatch in the side of your tube that you can use the hair dryer through when needed.
I'm pretty sure Mike did that mod on one of his scopes...
Al.