Thanks for the input everyone. Given the instability of the steelhead population everywhere, it seems like it would be safest not to support businesses that serve steelhead either because it would be nearly impossible to tell where it came from, whether or not they're wild or hatchery, and if the harvest is "sustainable". Given that many of us have trouble with agreeing on a definition of steelhead, it's likely the restaurant may not even really have a clue what they are actually selling or even just a marketing gimmick. I didn't end up going there, but if I did, I would at the very least, just not order that item. Another possible solution would be for everyone of us that lives anywhere near there to go to their restaurant and voice our objections to serving "steelhead". As a business, if they hear enough customer objections, they may just discontinue the practice to be on the safe side.
Incidentally, The Chum put up a post calling for a boycott of a restaurant serving wild steelhead
http://www.moldychum.com/home-old/2011/1/18/take-action-rays-boathouse-serving-wild-steelhead.html