I hear you on perceived danger of heating butane!
Having never made hash oil, I can't personally speak to the danger of using it to make oil but here are some interesting facts I found on
wikipedia. It says that butane boils at 0.5c, so i would think that the people on youtube cooking their butane are just being impatient. It should naturally evaporate at room temperature. For evidence of this i submit that when I was in high school some friends and i got a can of butane and used it to freeze stuff by making a small puddle and watching it evaporate almost immediately. I'm not sure if this would work with a larger quantity (like a whole can or three), but it might.