To me, playing dirty implies an intent to hurt or cheat. While Marvin does get quite a few fouls and has received a few yellows, his intent should never questioned.
Was Pete Rose a dirty player? (I know, wrong sport, but still a great example!) No, he was called Charlie Hustle and always played right on the edge. Marvin plays on the edge because he is competing in the middle against usually the most skilled player on the other team; in the spaces where the ball is most often (the middle); and the areas where successful teams always contest (defensive third) the hardest. Marvin will wear you out because he never stops competing. The match-up against Radcliffe last night was a classic example. Both players contested for ball. The referee let them play, only calling a foul when necessary. Both had a couple of knocks and had to be exhausted by the end of the game.