I too think the group should know about the quilt.
You can bring it to the next meeting as a "show & tell" finished item and have them decide if there's a problem with the quilting....
by simply not saying anything about it...just let them all look it over closely as a "pass around",
you can say, look, I just got this back and wanted to share it with everyone and have it turned to the quilting side
If no one says anything about the quilting, you could then mention (as if you just now saw it) the loose stitches. It may sound underhanded but it would avoid a direct confrontation to the other volunteers. They really do need to be aware of the problem so other quilters aren't left with the same issues you face.
Exclaim... oh my, how ever can I remove all these stitches by myself? Maybe several of them will whip out their froggers and start helping with the project of unquilting it then and there.
Laying a quilty guilt trip on you now....if the soldiers have to "confront" their fears and dangers, what's the worse that could happen if you "confront" the longarmer? You made a beautiful quilt for a thank you to them so give them a fair chance at giving you a silent thank you for the recognition of their services instead of you being embarrassed to pass it along. (off soap box now...btw, my son has been deployed 3 times so I feel strongly about this, it case you couldn't tell ... thank you for your efforts!!!!!)