Yes, vaping devices can and are used for illegal substances, but not commonly so. Not yet, anyway. Even if used legally by an adult, these devices are not acceptable at any school activity or on school grounds anywhere I am aware of.
So, can we move past that part?
Having some experience at the beginning of the vaporizer phase of medical marijuana and the study thereof afterwords, I agree. There are certainly vaporizers that heat the plant material to proper temperatures to obtain the appropriate THC analog in a vapor way. (I don't think analogue is the right word in chemistry. They are completely different chemicals that become gaseous at different temperatures.) While I don't know why (I suspect to make a marketable product.), THC for the modern vaporizers as discussed by the OP, seems to be a cartridge the device uses. To use that technology to get a THC dose, there either needs some manufacturing or a dedicated stoner willing to spend a lot of time making the correct mixture. A truly dedicated and literate stoner with a lot of time on his hands. I do not believe, without more, the OP's child is using the device for shenanigans.
Now, the issue of a legal vaporizer of a drug is more problematical. Some have used the second hand smoke stupid/lying rubric to outlaw them at some places. Just because the laws may be stupid/lying, do not make them unConstitutional. If there is a specific law making things illegal at a school activity or grounds, that is what it is and challenging it will take a boatload of money with an EXTREMELY uncertain result. (I think a loss, but don't see a case.) Personally, I also find them unacceptable to a youth facility. If I saw such a thing, I might also confiscate it.
An interesting issue the OP may explore is why his son needs a chemical device to deal with addiction and how that comports with the legal issues involved.
