The survival of the offspring of this inbreeding is minuscule but you make a good point.
For instance if a hatchery male fertilizes a wild females eggs then that negates those eggs because their survival is so poor.

ODFW has planted their broodstock "scum" throughout the Wilson river and so this interaction is facilitated by ODFW themselves.
Why do you think they opened the south fork after all these years?
The populations of wild winter steelhead were recovering in the Wilson and Nestucca rivers until the implementation of the steelhead broodstock programs and now are in decline. Volunteer to do redd surveys on either of those rivers and you agree.