I'm not sure. Something in the logic here seems off to me, but I can't find it. It may be partly that I'm not 100% positive that the vaginal ecosystem doesn't cause it to break down in such a way that would cause problems. I also think of all the people that say their infections are exasperated by glycerin. More research is needed!
Edited to add:
I looked up in my I Love Female Orgasm
book and it also said glycerin feeds yeast infections. Upon further research, I found this article
"Many personal lubricants, like K-Y jelly, contain glycerin which breaks down to sugars
and promotes yeast infections and possibly also bacterial vaginosis, noted Dr. Mary Marnach, a specialist in obstetrics and gynecology at the Mayo Clinic in Rochester, Minnesota." (Emphasis mine) I'm assuming a doctor that specializes in it knows what he's talking about. OK, they don't always, but I'm willing to make that leap here.
And this is what bothered me about the original article. "During metabolization, which is what the body does to break down food in its digestive system, glycerin can be converted to glucose by the LIVER. HOWEVER, glycerin cannot be converted to glucose in the vagina because the last time I checked, my liver was not attached to my vagina in any way, shape, or form!" This does not show me that the vagina doesn't break it down and some conversion happens. To assume that the vaginal ecosystem doesn't break it down because it's not a liver is a bit of a leap in my mind.
At the moment, I'm not convinced.