I just did a few quick searches and just about all of the references that I could find for Chlamydia/psittacosis was linked to birds. There was one that had a statement to include that mammals are at risk. I was not able to find any cases of this in sugar gliders. I am no expert and honestly...just searched for this information. Perhaps someone a bit more senior on the medical side can offer you more information. Here is a link to a veterinary article that outlines the transmission, symptoms, diagnostics, treatment, etc. I suppose if someone had birds near gliders and the birds had this...there could be a risk? I am just not 100% sure. I would imagine that you would have seen the other symptoms if this was an issue for your little guys though. Anyhow, enjoy that read!
www.nasphv.org/Documents/Psittacosis.pdf