Luckily, I found an open source project addressing exactly this issue, called x360ce. It integrates perfectly with Chrome. Just make sure to run the DirectX Web Installer before installing x360ce, install x360ce in the Chrome installation directory and run it from there for configuration. After restarting Chrome, the gamepad should work with the OpenROV cockpit. I also found that it is necessary to push one of the gamepad buttons while loading the cockpit software so that the gamepad is recognized.