Thanks for the link. Yes, it uses PG as the carrier.
I tend to think that if PG is the excipient in nebulizers used by lung transplant patients, as was claimed by a hospital employee told this by a thoracic consultant and who posted it here, then it must be fairly benign in even the most fragile of patients.
However it wouldn't surprise me if there is a gradual change to glycerine for all these purposes as in some ways it seems more suitable. Dow Chemical make all grades of both, and this is also what they suggest.