Outcasts are generally buddy-buddy with Bretonia, due to their mutual fight against the Corsairs and Outcasts. Rheinland, there are no friends there, but I guess? Just don't base off Kruezburg, too many Hessians there.
Corsairs are a no-no in Liberty. It's too far from home, and no friendly bases anywhere. Kusari is ok, but the Hogosha will generally chase you out and go "yeah, this tart is trying to ruin our relationship with you guys, discipline him or we will."
None of those options are wise, and Corsairs pirating in Liberty results in the admins beaming you back to Gamma with a warning. Remember that the Outcasts have no friends in Rheinland (even Kreuzberg operates on a "nobody likes you, so get what you need and keep going before we have an incident" level), and remember that the Outcasts are on half-decent terms with the Bretonians and the Corsairs are on half-decent terms with Kusari (Samura, mainly). Corsairs pirating Samura would be most unwise, seeing as Samura takes food down to Crete now and then... BowEx used to take MOX up to Malta too, until the war got closer to home.
I do not recommend any of them beyond "targets of opportunity".
Also, Mwerte, I don't think you meant to imply that the Bretonians and Outcasts work together to combat the Outcast menace. I lol'd.