I would correct this thread slightly: It's not specifically a Skyteam benefit, but you WOULD be upgraded as a result of the DL/AM cooperation agreement IF your ticket is on a codeshare flight AND your ticket is coded as a Delta ticket (006).
It doesn't come up often... but when you have a ticket like this you will be upgraded automatically and one day in advance. I have been upgraded on ORD-MEX and GDL-LAX in this manner.
You also will have access to their lounge in MEX as ST Elite+ with international ticket. And contrary to other comments in this thread, there is preferential boarding and it is honored in MEX.