Sure, that’s certainly possible. In fact, that’s what we do with our OpenSprinkler product — there the UI files add up to several MB so can’t be stored locally on the controller, and hence are hosted on opensprinkler server. In comparison, the OG UI files are much smaller. Generally we prefer to host them locally on the controller, because this way the system is self-contained, and even if you lose Internet you can still access the UI.
In the case of OpenSprinkler, we have customers who use it in a remote location with no Internet at all, so they will have to either use the OpenSprinkler mobile app (which has UI files built-in), or host the UI on a local server on their network. In any case, it just feels the system is not self-contained and relies on the existence of Internet. For that reason, when I designed OG, I chose to host files on the controller.