Regardless of wheather hatchery fish can reproduce in the wild it's not good to have hatchery fish spawning with wild fish. Therefore if you keep all the unclipped steelhead you catch you are doing a good thing for wild fish...
On that same token with the inability to know where an unclipped fish came from it's best to let it go and in most cases that is what is required by law.

In other words keep all the clipped fish you want there is no biological reason to ewlwase them and don't keep any unclipped..