"The annuity company says they won't compute the value of the annuity at the end of each year until the regulations are released by the IRS."
Without a year-end value, there is no way to determine by how much of the annuity payout exceed the RMD requirement of the annuity, so no way to know how much of RMD for the remainder of your 403(b) balance is satisfied by the annuity payout.
As to whether the annuity is still part of your 403(b) with payouts eligible to satisfy some of the RMD for the rest of the balance in your 403(b), it's possible, but that's a question for your 403(b) plan administrator.
