First the bad news, all of the emulators tested failed to see the buttons on the SNES or Genesis controllers. On the bright side, as Robert Broglia seems to have done all of the ports, if he updates his input handling to support the Retrode it would work across all of the tested emulators.
Now the good news, all the emulators tested work with the cartridges without issue! There is no setup required, you just plug in the cartridge and it shows up in your filesystem as ‘usbdisk’. That’s that. You can pick up SNES/Genesis/MS/GBA/GBC/GB/N64 cartridges confident in the knowledge that you can play them on your Ouya + Retrode.