Yep, it's 100% doable. In fact, you don't even need pumps, you can sometimes do it with a 1-tile hole designated as a pond and some buckets (it doesn't always seem to work).
I haven't tried filling reactors with buckets yet, but it would help to have a reactor pool at 7/7 producing power. Of course, when you have a reactor producing 10,000 units of power the 10 units of power for the pump are not going to matter unless you're using up nearly all of it. All of this testing has been done "Above Ground" so far, so I am going to do some testing underground.
Buckets may work because they "create" a 1/7 tile of water in the tile being filled a bit like pumps, aquifers, and rivers. I have actually tried turning off a pump system before and the flow seemed to remain.
Regarding the "brook makes all tiles flow," that may be true, but you definitely don't need a brook/river/etc to make the exploit work. Try it and see!
When I mentioned brooks and flow I meant they don't get gen'd through flow-stopping bodies of water (as far as I know). They don't seem to get gen'd in any world tile with a river or lake either.
If
people dwarves want power generated without windmills on embarks without flowing water, they seem go for the dwarven water reactor. If the 7/7flow reactor works, it will be more effective for powering 8-wide magma pumpstacks, since 12 or so waterwheels should be sufficient to power one over 100 z-levels, including power conduits, and that will fit in a 5x14 space over 2 z-levels.