Salmo can correct me if I am wrong, but here is my take on the experiment you propose. There are several control populations in this experiment already. Those are the ones not supplemented. The test populations were supplemented and the general result is very little change. As far as harvest effects (again, Salmo, check me out), these are Snake River Spring/Summer Chinook that for all practical purposes have zero ocean harvest, so the in-river harvest is all you have. Between 1979 and 2013, the total in-river harvest rate ranged between ~4% and 17%, and in fact in some years fish were left on the table. Given these figures, it's really hard to argue that changing harvest would have any effect since harvest is already very low and since putting additional fish on the spawning grounds (through supplementation) had little effect. Obviously this doesn't address any potential reduction in productivity from hatchery fish, but just about everything that I've read suggests that even hatchery fish will produce well if there is a lot of unused habitat.

Harvest estimates from: Snake River Harvest Module, June 2014, prepared by the National Marine Fisheries Service, West Coast Region, Portland, OR.