Thanks for posting your question. Delta hotels will not be a participating earning partner until February, 2016.
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Just called about missing stays in Marriott Rewards account with regards to Delta Hotels - and was told Delta is not a participating partner yet. CSR was nice but had obviously answered this question before. I mentioned that I booked the Delta stays through the Marriott Rewards site so assumed that they were points earning. Not so.
The integration team is working on the issue but do not expect to earn Marriott Points at Delta until well into first quarter 2016. Also not likely that they are going back to reward you for previous Delta stays. Something to keep in mind if you have other options.