Thought experiment. Let's suppose you're a CIVIL engineer -- the type of engineer the regulations are intended to target. You're on vacation in Oregon, and you notice a serious structural fault in a bridge which means that it is in imminent danger of collapse.
Under this interpretation of the term "practice engineering" you wouldn't be able to tell anyone because you're not licensed to practice engineering in Oregon. In fact anyone who found an obvious fault -- say, a crack in the bridge -- would be forbidden to warn people not to use it until it had been looked at.
Which is ridiculous. Having and expressing an opinion, even a professionally informed opinion, isn't "practicing engineering". Practicing engineering means getting paid -- possibly in some form other than money. At the very least it means performing the kind of services for which engineers are normally paid.
A law which prevented people from expressing opinions wouldn't pass constitutional muster unless it was "narrowly tailored to serve a compelling public interest" -- that's the phrase the constitutional lawyers use when talking about laws regulating constitutionally protected activities. In this case the public interest is safety, which would be served by a law which prevented unqualified people from falsely convincing people that a structure was safe. But there is no compelling interest in preventing an engineer from warning the public about something he thinks is dangerous or even improper.
So if the law means what they claim it to mean, it's very likely unconstitutional.