It seems to me that the idea of having a load not controlled by the MPP itself, connected to the solar array, is a bad idea. The job of the MPP is to control the load placed on the solar array to maximize output; anything outside of the MPP is going to 'dilute' this control capability.
Now the idea of an MPP that operates (say via a contactor) some direct loads on the solar array seems totally reasonable to me. In this way a smaller MPP could be efficiently used, operating some other 'loads of opportunity' when the power is available, without having to run the power through the MPP itself. In this case, however, the MPP algorithm and system would 'know' what is going on.
Regarding systems where the MOCV of the array exceeds the limits of attached components, but the normal operating point of the system is below the limits of the components: I think that this could be approached if you had additional safety components, at least as reliable as circuit breakers, which limit the voltage on any part of the system even with disconnects open. Because solar arrays have a well defined and limited short circuit current, you would need to have shorting crowbars rather than devices that open the circuit, but I don't see these as deal breakers. Possibly not worth the expense, but not unreasonable. If the duration of the DC over voltage is small enough, then it will put less stress on the insulation than the peak of the maximum allowed AC voltage.
-Jon