Hi Rick,
It depends on which box :smileywink:.
Almost all of our builds have GPU acceleration enabled, though we have released un-accelerated images of Debian, OpenWRT and Ubuntu over the years as pre-releases:
http://boundarydevices.com/imx6-builds
How to tell is difficult to answer without talking about the specific userspace.
Android has always included GPU support. Other userspaces often have the Vivante demos in /opt/viv_samples.
Debian and Ubuntu releases will generally have glxgears and the like as demonstrations.