My group haven't encountered glimmer wyrms in the main campaign yet, but they saw a few of them in the backstory oneshot we have finished some time ago. And specifically, they have encountered ones "employed" by the Golden Legion as the mounts for the Wyrmriders unit.

Another interesting fact about glimmer wyrms is that they have a very light-sensitive eyes, maybe a bit too light-sensitive for the waking world, but working perfectly fine at night, in darkness - or it the ethereal veil.

They also chirp and click, instead of a more expected hissing or roaring.