Brian, many of the men who served in Gaddy's company were too old or too young to serve in the Confederate army, but some of the men of military age had prior Confederate service, including 1861 volunteers and 1862 conscripts. If you're interested in more detail, I can work up a list of them.
Regarding other Arkansas Unionists, an entire company of the 2nd Kansas Cavalry was composed of men from Scott and Sebastian counties (excluding officers, which were Kansas men). I posted a roster on the Gerdes page several years ago.
I'll let you know if I run across any more. Michael Price has been doing some extensive and very interesting research on this subject, which I hope will result in a book.