Normally there isn't a pump in a reservoir, a reservoir being nothing but a tank with inlets and outlets for fluid, the pump is usually a separate component.
My concern is the impedence to flow inherent to meters and reservoirs, basically anything that has any kind of valve or fitting or even hard elbows. AIO pumps are such low pressure, low volume flow to begin with, any further impedence being detrimental to already lackluster performance. The exception would be in a FD or Swiftech design that uses a separate pump from the cpu block, not an Asetek or CoolIt pump/block combo.
If you have a reservoir with built in pump, I'd just do away with the AIO's pump altogether, replace it with a standard water block.
Gonna create some funky decisions on fittings as AIO tubing isn't standard diameters, either inside or outside, due to the needs of the ultra low evaporation rubber hose used as AIO's have a need for flexibility not common to even soft tubing used in custom loops.