There was a recent article on one mile at a time blog in January ("How Much Do Award Tickets Cost Airlines? You Might Be Surprised") with some insider info on how the accounting works on award redemptions between airlines. It is mentioned that payment rates are negotiated between airlines individually and are charged on a segment basis.

For revenue fares, the airlines that are part of JV partnerhips do revenue sharing on overall income between carriers on routes that are covered by partnership. This might influence award redemptions charges between them, but I wouldn't make too many assumptions.