I would expect that as long as the game is playable with a single Siri Remote, you will be just fine.
Forcing iOS support for multi player tvOS makes no sense at all, especially since there is no API for it.
From the guide:
Requirements for Games That Support Game Controllers
Apple has created specific requirements you must follow for any game that supports game controllers. These requirements are designed to make sure that games are always playable.
Your game must support the Apple TV remote. Your game may not require the use of a controller.
tvOS games that support controllers must support the extended control layout. All controllers for tvOS are nonformfitting extended controllers.
Games must be playable using standalone controllers. If you support an extended controller, the game must be playable solely with that controller.
You must support the pause button. All controllers include a Pause button. When gameplay is active, pressing the Pause button should pause gameplay. When the game is not being played, such as when you are at a menu screen, the Pause button moves to a previous screen of content.