UAL still does not have a joint contract. Continental scope barred any aircraft on the certificate (no matter who you operated them for) with over 50 seats. American has the same restriction, for now. If the Continental pilots prevail and keep their 50 seat scope in the joint UAL contract then the 900s will not be able to be on the same certificate as the Q400. Because these aircraft came in under the Continental contract and are operated in Continetal hubs they cannot be on the same certificate as the 900s for now until UAL has a joint CBA with new scope.

Continenal, United, Delta, and American scope apply to any aircraft on a certificate. The only airline that does not care what you fly for anybody else on the certificate is US Airways.

What is probably going to happen, however, is United management will prevail and United scope will be the scope in the new contract for UAL. Continental management has tried (and failed) to get rid of the 50 seat restriction for years.