Yes and no.
Direct Loans do not require a credit check and eligibility is not determined by your credit status. However, if you have a student loan in a default status, you may be ineligible for federal aid until the loan is no longer in default.
Graduate PLUS Loans will require a “soft” credit check. Lenders will review your credit report, though they will not look at your FICO score. The lender will be looking to see if there are any current delinquencies, defaults, or bankruptcies. If you are denied for Graduate PLUS funds, applying with a credit-worthy co-borrower can improve your chance of being approved for the loan.