Probably nothing they can do. Essentially, they'd get the same treatment for smoking spice as they'd get for using any other kind of illegal narcotic - and you don't see anyone getting second chances for smoking pot or doing any other drugs.
"In February (2011), Secretary of the Army John McHugh established an Army-wide policy prohibiting the use and possession of synthetic cannabis and other substitutes for delta-9-tetrahydrocannabinol, commonly referred to as THC, the primary psychoactive constituent of marijuana and substance in it that causes a 'high.'
...
"In regards to spice and other similar synthetic marijuana products, Soldiers from all components of the Army are prohibited from 'using, possessing, manufacturing, selling, distributing, importing into or exporting from the United States, or introducing into any installation, vessel, vehicle, or aircraft used by or under the control of the Army.'" ( http://www.army.mil/article/70316/ )