i have a vlamingi and a purple (among other tangs) in my tank, and they dont pay any attention to each other. vlamingi is in the same genus as a naso. i also have a clown tang - i think closely related to a sohal. the clown tang (3.5" long) sometimes chases the vlamingi (9" long) but doesnt care about the purple tang. i have heard that tang that are of similar shape or color have the hardes time getting along.