DURING LANDING ROLL; ORD ATCT CTLR INSTRUCTED MLG CREW TO TURN OFF AT TAXIWAY M-6. BEFORE THE CREW COULD ACKNOWLEDGE; TFC WAS OBSERVED AHEAD CROSSING THE RWY.

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ON BEING CLEARED TO LAND AT ORD ON RWY 09R WE WERE NOT ISSUED A LAHSO CLEARANCE; JUST; 'CLEARED TO LAND RWY 09;' WE EVEN VERIFIED THIS AT 1000 FT AGL BECAUSE I WAS UNSURE OF THE CALL. AS WE WERE ROLLING OUT ON RWY 09R; BETWEEN 90 KTS AND 80 KTS; WHICH WE STILL CONSIDER THE HIGH SPEED REGIME; WE WERE CALLED BY ORD TOWER AND ASKED TO TURN OFF ON TXWY M6; AT THE SAME TIME WE SAW A MITSUBISHI DIAMOND JET CROSS OUR RUNWAY AT TXWYS. WE WERE BETWEEN TXWY M5 AND TXWY M6 AT THE TIME OF THE CALL. WE WERE STOWING REVERSERS AND PREPARING TO MAKE THE TURN WHEN AN REGIONAL JET CROSSED RIGHT BEHIND THE DIAMOND JET. UPON CALLING THE TOWER AT ORD; THE TOWER SUPERVISOR SAID THAT THEY; TECHNICALLY COULDN'T CLEAR US FOR A LAHSO OPERATION BECAUSE THERE WAS A 4 KT TAILWIND. BUT THAT THE TOWER CONTROLLER THOUGHT THAT WE WOULD BE SLOWED ENOUGH THAT HE COULD CROSS THE 2 AIRCRAFT. I BROUGHT UP THAT THE DIAMOND JET WAS ON OUR RWY BEFORE WE HAD ACKNOWLEDGED BEING ABLE TO MAKE TXWY M6 AND THAT IF WE HAD A HYDRAULIC MALFUNCTION THAT THE OPERATION COULD HAVE BEEN A REAL MESS. HE TECHNICALLY COULDN'T GIVE US A LAHSO CLEARANCE DUE TO THE TAILWIND BUT HE DID THE OPERATION ANYWAY. THE RUNWAY WAS LEGALLY OURS AS THE LANDING AIRCRAFT AND A RUNWAY INCURSION OR TWO WAS CAUSED BY ORD TOWER.