I'm currently pursuing a waiver for psoriasis as well, though mine is for the Navy NUPOC commisisoning program and my psoriasis is very mild. From your description I would unfortunately say your example is not likely waiverable, as you admit openly that is is "pretty active" and it "does flare up when I'm stressed or in dry conditions." The docs who will review you are specifically going to address those two points, and they want to see/hear the opposite.
That said, your answer will definitely be a "No" if you never apply. I'd go see a dermatologist and get a current clinical opinion on the condition. If you can't get in to NROTC, but the dermatologist thinks you could get to the point of waiverability with treatment, you could always try OCS after college or one of the commissioning programs like NUPOC. The end goal is a career in the Navy, and many roads lead to that destination.
