RAT powers blue system, which then runs the emergency generator.
HYD B ELEC PUMP LO
PR OVHT = electric pump has failed, but the hydraulic fluid is still there. If you deploy the RAT, it will still power the emergency generator
HYD B RSVR LO AIR
PR = the air pressure is low, which might cause hydraulic pressure to fluctuate, especially when manuevering and at high altitudes, but enerally it should still provide normal flow to the pump. No difference on whether you use RAT or the electric pump to pressure the blue system.
HYD B RSVR LO LVL = no or low hydraulic fluid quantity in the blue system. If the RAT deploys, it can't power the blue system, since there is no fluid. No blue system = no emergency generator.