Incidental Catch is one thing, angling for a specific species is another. We do not angle for trout with a 2 hand, 13' 7wt rod and large fly. You have to draw the line somewhere and that is where it is drawn. If you are using steelhead gear, you are fishing for steelhead. I believe this is essentially the legalities of the rules.
As a side note, I think that at least some of us wish there could be more discretion with the way law enforcement folks deal with us. This, in a small way, is exactly what we have here. If I am engaged in a questionable practice and I tend to act like a, well..you know..when questioned by a ODFW officer, I can expect that any decision they make regarding myself to be negative when they have a choice.
Beyond the stated rules, there is the spirit of the law. There are going to be circumstances that are open to interpretation, but those of us here know what the rules are. You need to have an ANGLING permit to fish in this state. Even if you cannot catch anything....If you should happen to catch and land a steelhead on your 3 wt, simply release it. Having a fish in your possession means removing it from the water (say, for a picture). If you release it in the water, there should be no issue.
I have a certain loss of respect for those who fish but do not care to follow the rules, GOOD OR BAD. When you fish in this state, there are rules that need to be followed. I don't care for all the rules either, but I need to live with the bad ones...or work to change them. There are some fine folks that work for ODFW and they they struggle to try to make things right. Many of them feel the same way we do and they try to make changes from the inside. This is more than I do......
I follow the rules wherever I fish. I do not look over my shoulder, I do not mind seeing Law enforcement in my area and I never mind seeing other anglers watching me. I am spending my time enjoying my fishing. I am not known as Mr. Morals.... but I KNOW THE DIFFERENCE BETWEEN RIGHT AND WRONG and have no need to labor with my own personal interpretation of the rules while enjoying my pastime. The legalities are not going to be changed while I am on the water anyway. That is for another time.
For the record, I do not care for all the rules in effect either, but I am going to play by them.

Whew!

Morality and law are seldom the same. Especially when you are talking about for profit wildlife management.

That said, my inspiration for posting the original question was that I wanted to be legal, however didn't want to spend money if I didn't have to.

I now understand that the Salmon/Steelhead Tag is needed, whether or not I keep fish, or even catch any. Thanks.