I just called 1-800-375-5283
After I reached CSR (a lday), we had following conversation after I told her my WAC number.
me: Can you tell if my name check has been cleared or not?
CSR: I don't have personal information to tell you.
me: Huh... FBI name check is every important step to get I-485 approved. You don't know if my name check is cleared?
CSR: That's right, I don't have your personal information to tell you.