I don't know how useful it would be here but back in the days when I was playing SAMP on a Cops & Robbers server, Army used to assist the police with day to day duties and higher profile criminal activity. They also had access to better weapons (automatic riffles, snipers etc..) and the Hydra, Hunter and Tanks.
If Army does end up getting introduced they would probably have to adjust the times and complexities of the crime jobs, otherwise it would be to hard for the criminals if you get police + army chasing after you