AN INSTRUCTOR PLT AND PVT PLT IN A PA34 ON AN ILS TO RWY 26R AT CNO HAVE A POTENTIAL CONFLICT WITH AN OPPOSITE DIRECTION MOONEY AT 2500 FT ON AN ILS APCH TO RWY 9 AT RAL; CA.

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WHILE PRACTICING APCHS AT CNO; CTLR GAVE A VECTOR OF 360 DEGS TO 350 DEGS. THIS IS USUALLY THE SECOND TO LAST VECTOR TO INTERCEPT FINAL FOR THE ILS RWY 26R APCH AT CNO. HOWEVER; THE CTLR DID NOT INFORM US THAT IT WAS A VECTOR ACROSS FINAL UNTIL I MADE A RADIO CALL TO GET THE CTLR'S ATTN. WE FLEW CLRLY THROUGH THE LOC AT 3000 FT AND THEN THE CTLR GAVE US INSTRUCTIONS TO TURN L TO 210 DEGS; INTERCEPT THE LOC AT OR ABOVE 2100 FT CLRED FOR THE APCH. I THEN READ BACK THE INSTRUCTIONS; '210 DEGS; 2100 FT; CLRED FOR THE APCH.' MY STUDENT QUERIED ME BECAUSE THE CLRNC TO DSND TO 2100 FT WAS NOT A NORMAL CLRNC. I POINTED OUT ON THE APCH PLATE THAT THE MDH BTWN LINDN INTXN AND DEWYE WAS 2100 FT. WE DSNDED TO 2100 FT TO INTERCEPT THE GS; AND WHEN WE BEGAN LEVELING OFF; THE CTLR CALLED BACK AND ADVISED THAT WE WERE TOLD TO DSND TO 2800 FT AND THAT WE HAD A TFC ALERT FOR A MOONEY SHOOTING THE ILS RWY 9 APCH AT RIVERSIDE. I REPLIED THAT I HEARD 2100 FT AND READ BACK 2100 FT; BUT WOULD CLB IMMEDIATELY TO 2800 FT. AS I CLBED; I SAW THE TFC; WHICH WE MAY HAVE HIT IF I WOULD HAVE REMAINED AT 2100 FT. I BELIEVE THE ERROR WAS CAUSED BY THE CTLR; BUT ALSO BELIEVE IT IS VERY DANGEROUS TO ALLOW PRACTICE APCHS AT THESE ARPTS SIMULTANEOUSLY.