You would (probably) need some way to connect the two Hubitat hubs. Hubitat has a pair of built-in apps called Hub Link and Link to Hub that could work for this purpose. A more powerful community solution is HubConnect. Either lets you share devices from one hub to another (HubConnect lets you go in either or both direction, supports more types of devices, can sync modes and HSM status in either direction, and has lots of other features, but it does require the installation of custom code, for which it does have clear explanations if you are not familiar but would still require carefully following them). This would let you use devices from one hub for the purpose of automation (apps, rules, etc.) on another.
Of course, you don't need to do this if all of your lighting automations can be self-contained on that hub. For example, if all your Zigbee bulbs fit on that hub and you don't need to reference any devices from the other hub, then you wouldn't need to. But this is probably unlikely--for example, maybe you have Zigbee motion sensors you'd use to automate (need to be on a different hub). Even if your sensors are Z-Wave, you'd likely at least want a repeater or two on that hub for Z-Wave (which you may or may not want to use for a "real" purpose there or somewhere else).
I think a Hue Bridge would be the best option here. It's easy to integrate Hue bulbs (or groups) into Hubitat with the built-in integration (or a couple community options, one of which is mine), so you wouldn't have to worry about connecting to Hubitats (again not hard, but the bulbs are really easy to set up on Hue since its only purpose is lighting, and everything you need to get them into Hubitat is built in). I've also tried a dedicated bulb-only Hubitat, and a couple Crees (which I also have) still managed to fall off it--but they've been fine on Hue. It's also a bit cheaper, and you can probably find a used or even new or like-new one on eBay for even less.
