ACR X HAD CONFLICT WITH DC-9 MAKING PRACTICE APCH TO WRONG RWY.

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ACR X AT 8000 FT MSL WE WERE SWITCHED FROM RWY 25L TO RWY 25R TO TRACK LOC INBOUND. WE WERE GIVEN TFC 10 O'CLOCK 5000 FT. WE REPLIED LOOKING; NO CONTACT. ONCE CLR OF THE THIN CLOUDS AND WITH ARPT IN SIGHT; I CALLED ARPT IN SIGHT AND TOLD APCH WE HAD TFC LOW AT 12 O'CLOCK. THEY CLRED US FOR A VISUAL AND SAID THAT TFC WAS DC-9 FOR THE L RWY AND THAT WAS THE TFC WE HAD RPTED IN SIGHT. I CORRECTED THE CTLR AND SAID WE HAD NOT RPTED ANY TFC IN SIGHT. DC-9 WAS CONDUCTING TRAINING AND I THINK HE HAD THE WRONG ILS DIALED UP. HE STAYED AT OUR 12 O'CLOCK; EVEN AFTER WE ALTERED COURSE WELL TO THE R OF RWY 25R. HE SAID HE WAS CORRECTING. WE GOT TCASII ALERTS; BUT HAD A GOOD VISUAL ON HIM. TWR WAS CONTACTED AND CONFIRMED HE WAS FOR THE L AND WE WERE FOR THE R. WE STAYED AT HIS 4-5 O'CLOCK AND 100-200 FT ABOVE HIM TO TOUCHDOWN. HE FINALLY GOT LINED UP FOR THE L AT ABOUT 1200 FT AGL. I THINK HE SHOULD HAVE BEEN TOLD TO GAR. IN RETROSPECT SINCE HE DIDN'T; I PROBABLY SHOULD HAVE HAD THE FO GAR. THIS WAS A LITTLE CLOSE UNDER GOOD DAYLIGHT CONDITIONS; BUT WITH THE DC-9'S ERRATIC FLYING AND NIGHT TIME; A GAR WOULD PROBABLY HAVE BEEN PRUDENT EVEN THOUGH WE WERE LEGAL TO CONTINUE AND LAND. ON LNDG THE TWR TOLD DC-9 'GOOD JOB' AND CLRED HIM TO TAXI BACK FOR ANOTHER PRACTICE APCH. HE TOLD US TO CROSS THE 'R' AND CONTACT GND. WE INFORMED HIM WE WERE ON THE R RWY AND HE SAID OH; OK; CONTACT GND. THIS SCENARIO SMACKS OF A MAJOR SCREW UP WAITING TO HAPPEN IN LAS. LAS ROUTINELY TRIES TO GET YOU TO CALL TFC IN SIGHT WHEN THERE ARE NUMEROUS TARGETS. I REALIZE THE TIME AND SEPARATION CONSTRAINTS THAT THEY WORK UNDER BUT; IT IS BEST TO NOT CALL IN SIGHT AND LET THEM KNOW YOU DEFINITELY CAN'T IDENT THE TFC THEY ARE CALLING OUT UNLESS DAY VMC.