Yes, you can play Mario Kart with two 8bitdo Micro Gamepads on your Mac in the Cemu app. Cemu supports the configuration of multiple controllers, and you can make separate assignments for each controller in the input settings. Set the emulated controller to "Wii U GamePad" and the API type to "SDL controller". You can add and configure additional controllers using the "+" button.

The 8bitdo Micro Gamepads are compatible with Mac and support both wired and wireless connections via USB or Bluetooth, which enables use with Cemu on Mac. Note that for motion controls in Cemu, support varies depending on the controller, but the basic button mapping for Mario Kart should work fine.