Welcome to the forum! You can check the regulations in the forum headings. And, yes, you definitely need an Oregon Fishing license. It will cost you since, I assume, you are not a resident here. But the cost pales compared to getting caught without one and having all your gear confiscated and then receiving a very hefty ticket.
Great place and I'd love to go back. Check out pictures from a trip I took there back in '08 in my profile. We base camped at horseshoe and hiked to Douglas and Moccasin on a day trip. I think you could catch fish all day long with floating line and a caddis fly. I don't recall the regulations but I was letting them go anyways. Have fun up there and if you go in from Wallowa Lake, 6mile camp seems like 10mile camp. My son and his buddy were 19 years old at the time and they were pooped by the time we got there. Make sure you stop and perhaps take a Wallowa shower in the waterfall on the way up to Horseshoe.