Yes Marriott has an Ambassador status (I found this out when they sent me a little black box). I would try to inquire through SPG.
Here is my hunch, SPG and Marriott might keep the requirements to Ambassador separate. I know they gave out automatic status up to Platinum, but might be holding the highest level to those who 'earned' it. Conversely, I didnt automatically get Ambassador status at SPG and dont know if it could be had with a phone call.