Where did you hear that?
I'm not an expert but I believe its the OPPOSITE. (I do have 18 GBBP's and 6 GBBR's which have zero issues using Ultrair)
Gas guns NEED to have the oil in the gas to protect the seals in the magazines. (That's why all airsoft gas has some silicone oil mixed in)
You just clean the barrel and hop rubber after heavy use. Use Isopropyl Alcohol on a strip of cloth with the cleaning rod. DON'T go into the hop rubber. Use a Q-Tip with a drop of Isopropyl for the hop rubber.
Dry gas such as Propane needs silicone adding to it because its not meant for airsoft and without added oil the mag seals will dry up resulting in leaks and needing replacements...
The only reason some people use Propane is because its cheaper than green gas. The airsoft fill adaptors have a port to add the silicone oil.