I have figured out why Sgt. Chuck the Techie got invited to go to Atlantis.
Exhibit A is under the cut.
Look at the ear. He is clearly of elfish Alteran descent, much like John Sheppard. While it is not as pointed as Sheppard's, there's certainly a point there, enough to put him higher on the scale of Ancient Geneosity than say, Carson, but lower than Wonder Boy Shep.