Neither a gay marriage or civil union initiative would pass in WA. They would probably have a struggle just to gather enough signatures to get it on the ballot. Their only hope would be for the legislature to pass a modification to the DOMA that would then would be tested in the courts for constitutionality.
Gay marriage might be a tough one, but civil unions, you'd get enough signatures just in the cities that have colleges. As for a general election, remember that WA twice passed fairly liberal abortion laws, the first time in 1970 and the second time in 1990 (ultraliberal, just in case Roe v. Wade got overturned). While the initiatives have shown some conservatism, its fiscal conservatism only. Remember the "Hands off Washington" campaign regarding gay rights? That one passed.