I believe it is a mental state, and it is subjective by nature. You need to feel some compulsion towards gambling, maybe that need to experience the swings, the adrenaline rush, that lack of judgment of knowing it´s -EV and still doing it, or being dumb enough to not even know what a -EV game is, to be a degen. So, in my own definition, you can be a winner and a poker degen at the same time. A pro who is not a degen is the responsible guy who always take the rational approach: good BRM, treats poker for what it really is: a boring grind where winning means making as many good decisions and as few bad ones as he can humanly make for his skill level, do not let the swings affect how he plays, work on his game constantly, etc. Only obvious stuff really
I don´t think you can be a no-degen pro at poker and a degen in any other gambling, as the mental flaw is the same. -EV gambling is just irrational, doesn´t make any sense.
Edit: so yes, a winning poker pro who goes to the roulette should be a degen