1) After memorizing a "non-recital" piece hands separate, is it "cheating" or inefficient to look at the score when putting hands together (as opposed to memorizing hands together without looking at the score)?
2) Once a piece is memorized hands together is it non-beneficial to look at the score while playing? Should one only refer to the score to check for accuracy or is it okay to play from the score to trigger reminders?
But, I'm not absolutely sure why you would want to learn a piece from memory hands separately.
However, this applys only to "beginners". Experienced pianists don't usually do this, unless they want to analyze a piece in every detail. If you can play everything at sight and hands together, there is no need to do any of this. If you can't, starting with hands separate has a lot of benefits.
True. One exception I see for advanced pianists is the fact that in learning more difficult passages, it is often helpful (if not absolutely necessary) to work hands seperate. This includes places where excellent technique is required, places where the melody should be voiced more expressively and other places too numerous to mention.