Yes M1 comes from the factory and is a Dexos oil.
Here is a full listing of approved GM Dexos oils that can be used on your SS:
http://www.gmdexos.com/licensedbrand...sedbrands.html
As for GM easy care, I would imagine it's based on the package you purchased, that's the level of oil you'll received. Remember synthetic is recommended for these cars, not required. As long as it Dexos, that's all that matters when it comes to your warranty.