BFR DEPTG TUCSON, AZ ON A RETURN FLT TO LONG BEACH, CA, 2 STUDENT HELICOPTER PLTS (THE OWNERS) WERE ADVISED VFR FLT WAS NOT RCMDD DUE TO LOW CEILING/VIS AT THE DESTN. NEITHER PLT WAS ENDORSED FOR X-COUNTRY FLT. EN ROUTE, THEY LNDD/REFUELED AT GILA BEND & PARKER, AZ. AT 2124 PST, THEY TOLD TRACON THEY WERE VFR AT 4500' & RCVD VECTORS TO LONG BEACH. HOWEVER, DRG ARRIVAL, THE ARPT WAS NOT VISIBLE DUE TO A 500' OVERCAST. THE CREW RPRTD 40 MIN OF FUEL REMAINING & REQD VECTORS TO THE NEAREST ARPT WITH VFR CONDS. ONTARIO INTL & NORTON AFB WERE THE ONLY ARPTS IN THE AREA WITH NO CEILING; BOTH WERE RPRTG APRX 1 MI VIS WITH FOG & HAZE. THE CREW DIVERTED TO ONTARIO & WERE CLRD FOR A SPECIAL VFR DSCNT TO RWY 26L. ABOUT 3 MIN LATER, WHILE DSCNDG THRU 2000', THEIR CLNC WAS AMENDED DUE TO POSSIBLE CONFLICTING TRAFFIC. SHORTLY THEREAFTER, RADIO & RADAR CONTACT WITH THE ACFT WERE LOST. AT 0151, THE ACFT WAS FND APRX 1 MI SOUTH OF THE ARPT WHERE IT IMPACTED IN A NOSE LOW, LEFT BANK ATTITUDE. TESTS SHOWED 1 STUDENT (PRESUMED 2ND-IN-COMMAND) HAD A BLOOD/ALCOHOL LVL OF 0.160%.