IF they choose to do it - and it is a big IF - they can but they will have to manually generate a tag for you. None of the carriers have a system that can generate a tag for a 6 flight routing automatically. And I'm pretty sure that the official policy is seamless handling of bags across carriers on a single ticket, not three tickets that are booked end-on-end. You'll need an agent who REALLY knows what they are doing to make it happen.