2 or 3 axis A/P?
about which boeing models are we talking?
you mentioned a sideslip which would require a 3-axis A/P to operate the rudder.
i only fly the 'primitive' B737 with a 2-axis A/P + yaw damper.
judging from my sim experience you can "assist" the A/P using the rudder. it will counteract any input with the ailerons to maintain track or whatever.