FAA "Safety Pilot"
If you are under the hood working on some form of "instrument proficiency" with a non-CFII in the right seat then you are quite likely making a VFR flight.
VFR flight requires that the pilot "see and avoid," something that can only be done by the safety pilot in this case. The safety pilot is the PIC even if the guy/gal under the hood is the sole manipulator of the controls and may also log the time as such.
The moment the hood comes down the ability to "see" goes away. N'est-ce pas?
So, that begs the question - can two pilots alternate right/left, seat under the hood, etc. so that both of them can accumulate 50 hours of cross country flying with only a total of 50 hours a/c rental? Seems like it should work...
Terry