To me this is the equivalent to Tyson showing up at WM in 1998. Both of them were still huge names but realistically at down parts of their career. Rousey much more than Tyson. But they were at such an amazingly high level that it could be a while before they hit low.
Now Rousey as a pro wrestler could really suck because as anyone who watched the UFC she was basically one dimmensional. Granted it might be because of awful coaching which shouldn't be an issue in the WWE. But her marketability will more than compensate for shitty matches in the beginning