Migration Assistant not recognizing ethernet
Okay, here we go

It's a simple answer, so...

After wasting hours of time trying to figure this out I realized that Migration Assistant is not smart enough to set up the Ethernet connection itself.

I had to go into System-Preferences->Network and add and manage the Ethernet.

I then turned off the wifi, turned on file sharing, and was able to see the other computer coming from the other side.

Even though all the tutorials I had read said "just plug in the Ethernet cable and go" (in my own words), I still had to set it up manually.
Oddly enough, the MacBookPro didn't even have the default Ethernet settings.

Hope this helps someone else!