definitely

the two babies I housed alone were flighty and didn't eat much until I put them together, then they were perfectly calm and fearless and ate relentlessly for the rest of their days.

my WC adult (red sided) was housed alone for years and was always flighty, hid most of the time, and didn't tolerate being held.. within months of putting my concinnus, who is ridiculously calm and friendly (that may or may not have anything to do with it) with him he became almost as calm and bold as the concinnus, although he still doesn't like being held. He also started eating more than all my snakes. Immediate change.

I hear it from others all the time too. I'll always house garters with another of the same sex if I can. I think they're programmed to be communal.