The second draft of the script (dated Sep 24, 1973) is also the latest draft as Coppola began filming on October 1, and so can be considered canon. I've never checked this scene out in the script. So this proofs that Roth did in fact wanted Pentangeli to remain alive, and so Tony Rosato's line makes perfect sense.
"It was between the brothers Kay -- I had nothing to do with it."
