Think of it this way: High grades might help, but they won't get you in without the talent. Low grades will almost certainly disqualify you regardless of talent, but strong grades alone won't guarantee admission.
Therefore, the answer is: You need to demonstrate exceptional talent in your chosen art field *and* maintain acceptable academic standing, although the specific academic requirements aren't publicly stated as a cutoff GPA. The application and audition process are rigorous and designed to select the most promising students.