ltl cleo, I think that in a situation where the spawning habitat is limited, the coho and steelhead would compete for spawning sites. Generally steelhead dig deeper redds and spawn later, so there could be danger of the hatchery steelhead digging up the coho redds. The two species usally spawn in different areas, so my guess would be there wouldn't be too much to worry about unless there is very little spawning gravel. But, I don't know the area and if you have seen them in spawning areas at the same time, they are probably competing for redd sites. I just don't know enough about these early runs of hatchery fish, other than they have very poor reproductive success, to make an educated guess of how they interact with coho. It is an interesting question, you should give the WDFW a shout, maybe they can start a research project to give a definitive answer to this question
Get out and fish!