I have to walk back my too early in the morning, before I've had any coffee statement.
I've read that it works for Southwest, but I'm not sure about other airlines.
If you try to use Amex's Use Points for Charges feature by yourself, you'll see a redemption rate of only 0.6 cpp even on charges booked directly with an airline. In the MMS example, they had to call in to Amex Travel to get the reimbursement at 1 cpp.
Not wanting to rely solely on MMS, I chatted with Amex this morning. The frontline Amex rep told me MR are 1 cpp for flights booked on Amex Travel, but 0.6 cpp for flights booked directly with an airline and reimbursed as a statement credit. I asked him using Southwest as an example, and Amex's own faq answer that tells you to book directly and then redeem points for the charge (and not mentioned, MMS's dp that it redeems at 1 cpp). The Amex rep basically told me I should always check first with Amex Travel how points will be redeemed for charges before booking directly, because Amex Travel can help book the flight over the phone at 1 cpp.
So TL;DR -- using MR points can be complicated, call Amex Travel first.