Online Forum for the 2012 Rav4 EV

Yes, the fourth pump is the cabin heater pump.

I think that the pumps fail more often than they do on ICE vehicles because, while an ICE vehicle runs its water pumps only when driving, an EV runs them when charging, too. Since charging is at fewer MPH than driving, they run them >> more.

As for not being familiar with the innards, neither (blissfully) was I until a few weeks ago. It was a learning experience born of necessity. The basic diagnostic service on this would have been $869 through the dealership. Then the cost of the part alone would have been >$500+tax. I think it could be done in one shop hour (~$100).
So >$1400 for a damned water pump.
-Davio

A trained technician will analyze (diagnose) your concern. As a result of diagnosis, an estimate for repairs or additional diagnosis as required will be provided to you. Diagnosis fee does not include cost of parts and/or labor to complete repair. Please address any concerns directly with your service advisor upon arrival.
Disclaimer regarding price:
Waived if covered under factory or extended warranty. Dealership will determine eligibility.

This is what Toyota of Palo Alto says about the service:As for the part, thanks. Yes, that would save me a few hundred dollars off of the Toyota of Walnut Creek price. I would still certainly like to know if the parts are truly identical or are merely interoperable.
-Davio
UPDATE: To be fair, on another tread a person with an EV charging malfunction much like mine reports that the diagnostics cost $160 at Tustin Toyota in Orange County, CA.

... But since they would want to provide service based on the diagnostics, I would assume that they've provide enough information at least to explain what they would do to repair the car and why. Perhaps they'd provide a report similar to the one that you posted.
-Davio