They are tied in together. Your skater is one guy and no matter what position you play or whether you play OTP or EASHL...you get graded each game. As far as I know...your grades/overall grade is only based on the average of the last 10 games you played
(but I might be wrong about that).
Though...when you check the leaderboards, they have broken down the rankings/stats into 2 seperate categories OTP and EASHL.