I just talked to our pass bureau lady, and she was able to give me a little more definite of an answer than last time. If the routing is the same, different carriers WILL accept any ZED pass, ie LAX-LHR is good on BA, VS, and AA. Different routings are where it gets sticky. From the sound of it, though, LH allows different routings within the same fare zone, ie PDX-FRA and SFO-FRA.