Same as white, green, yellow, black, pu erh tea, and all of their different varieties within those categories, it's all the same leaves, just different processes.
Well, not exactly in that there are cultivars and farm differences. In that way it is a little bit like grape wine, where different processing can produce very different wines from the same grapes, but there are also differences in grapes that can come through within a style.
In a way, yes; Wuyi rock oolong will be different than a high mountain Taiwanese oolong. But what most people think of as green vs black tea, they don't realize that it's the same exact plant. Camellia sinensis has only 2 cultivars, var. sinensis (the main one) and var. assamica.
