I was wondering if it's possible to have the same IP for 2 different MAC that is on the same machine. For example having the ethernet and WiFi MAC address for my MacBook for the same IP address.
It is not possible. Once it is set in the AirPort Utility to one MAC address, it won't allow you to assign it to another MAC address. You'll get an error.
This makes sense because you can have the Ethernet and Wi-Fi enabled at the same time.
If you would assign the same IP address for both interfaces (Ethernet & Wi-Fi) you could create a conflict resulting in not being able to make any connection at all to your device.