A veteran is not enough in Oregon, you need to be a disabled veteran and have a letter from the VA confirming it. Even having the DAV card from the VA health care system is not enough - you must have the letter in Oregon.
Anyone that is a disabled veteran gets a letter from the VA every year confirming your status. That's the letter you need for most disabled veteran discounts in any state that offers it.
One thing different in Oregon, and is unusual as it's the only state that I know of that requires the veteran to submit the letter and get the card in the mail. All other states that I know of, you can carry your paperwork in, and that does it. Some states give you a card, some don't - but most will give you the card or the discount across the counter if you have your letter.
Texas for example will give you a card that waives the 'day-use fee', but not the camping fee. And Texas gives you a lifetime card same day you show the letter. Each state has different rules, so it pays to research it BEFORE you go and camp if it's not your home state.
Every little bit helps nowadays, as some states are raising fees and now charging day-use fees even if you camp. And some discount the day-use but not the camp fee, and some discount the day-use and the camping - all different scenarios across the USA.