they're bugged, i think. they are probably supposed to be SIG/LeFH spotters (with attendant offtable batteries) but they aren't.
in the GT:OS shilovo campaign, there were no such "artillery spotter" units. everything was either SIG/LEFH/MRS18 as normal.
Yes, one spotter was defective. In last update it has been corrected (need to restart operation).