they will probably have more customers like most hospitals. Which means waiting times can only get worse for Kaiser. However, some hospitals/doctors are more directed to small group health insurance (Sutter or Western Health Advantage are two examples). While they may also deal with more customers I can't imagine it being as bad as Kaiser since they are not really competing on the exchanges.
So if United has some of these doctor groups or hospitals in their networks then you may get better service with shorter wait times. This is just me guessing so I may be wrong.