Your tax return does not report anything that specifically associates your distributions with RMDs. There is no need to indicate that any particular IRA's RMD was satisfied from any particular source. Your tax return simply shows on Form 1040 line 15a (or 15b if the entire amount is taxable) or Form 1040A line 16a (or 16b if the entire amount is taxable) the total of your distributions.
I assume that you annuity is an IRA deferred annuity. Yes, provided that your IRA annuity had a 2015 year-end balance (was not annuitized) you can aggregate the RMDs separately calculated for each of your traditional IRAs, including the IRA annuity, and take distributions from the IRAs in any combination to satisfy the aggregate IRA RMD.
