The three rescue mods that I know of, and have used personally, "work" so to say. They can be buggy and sometimes a general pain in the ass but if you really want to play as a firefighter, ems, or as the coast guard I'd give "Rescue Mod V (FD + EMS + Coast Guard)", "Firefighter Mods (Mode Sapeurs-Pomppiers)", and "EMS Mods 0.8.4 BETA" a try. They can be found on gta5-mods.com and lcpdfr.com