Yes, you are correct, pikeminnows are predators of salmon and steelhead smolts and benefited from the impoundment system on the Columbia.
I used to follow salmon issues pretty closely when I lived out there, but not anymore. My 2 cents is that salmon don't do well in a landscape with dams, cities, farms (irrigation), dikes and levies, container ports and everything that comes with a large human population. Then you throw in fishing pressure for fish that can bring over $20 lb. for fillets.
I've watched salmon recovery efforts in the Pacific NW for 35 years and it has been mostly a story of failure. About a billion $ per year is spent on Columbia system salmon recovery, it has become something of an industry and if it isn't working too well, it does provide some make work jobs.
I'd like to believe the fish can come back, but I doubt they will.
The pikeminnow deal has been going on for something like 25 years at least. It doesn't look to be making a difference. But once programs like this get started, you can't kill them off.
Pikeminnow aren't that easy to catch, anyone making $100K is doing well.