Sex-link birds are 'sexable' because of differences in chick and adult coloration so to answer your question both cockerels and pullets are sex links - What variety of sex link do you have, and what color is the chick.
Yes there are sex link roosters. That's supposed to be the point of sex link chickens. At birth the females are a certain color and the males are a certain color. That way you can sex them simply by their color. Doesn't always work out perfectly though. I have 20 red sex links. All looked alike for the first 2 weeks then 1 turned white. He is the rooster. We kept him anyway.