I know one who does both. She is actually quite good but probably makes only a single digit percent of her income on stock. Mostly her portfolio serves as a starting point where clients say, "like this one only of my subject".
The stock photo industry is getting bigger, while profit-per-photo is plummeting. There are still a number of well-known photogs in this space, some of whom are doing remarkably well for themselves.
My impression of that industry is that it's all about process - to make a living doing it you need to have an extremely streamlined process and churn out a vast amount of work.
You don't know any stock photogs?