I am going absolutely insane trying to figure this out. I've searched through the forums, but I have not been able to find anyone who is trying to get a CC character into Mixamo.
At present, I've tried all options for export from CC, and the character does not import properly.
I read in one forum response that you could use 3DX to export the character so it is compatible with Mixamo, but my "Convert to Non-Standard" button is grayed out when I attempt this.

Does anyone have a workflow or tutorial for CC -> Mixamo?

Thank you.

Just out of curiosity, what would be the advantage of sending a character to Mixamo? In other words, what would be the application?

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This is where my issue arises. If I use the Maya preset, Mixamo will import the model sometimes (if it does not succeed, Mixamo simply states "Sorry, unable to map your existing skeleton."), but animations will not apply. The closest preset seems to be Unreal. The model imports and animates using the Unreal preset, but there's an issue where the head jitters.

So are you using UE4? You just use the auto-setup for UE4, and then just export your character and animations from CC3 Pipeline.

Late but I finally found the solution. I too was having the same problems as you. I had to have the avatar in t-pose and in the include motion I had to check 'current pose' and 'first frame in bid-pose" 

Thanks! Following this settings, I was able to import the CC3 Model in Mixamo and Accurig. Then exported the FBX file for Blender. But the strange thing is, the imported model's Bones is incompletely rigged. Some parts are still disconnected and does not have IK. Is that normal? Do you have other tips on what to do next to properly set up the rig?