Zigbee bulbs in general don't repeat very well and cause mesh issues. Hue light bulbs for example... There are Zigbee bulbs that do not act as repeaters that would work fine. As for linking hubs there is an app you can install to control multiple hubs called HubConnect.
The Hue hub connects to Hubitat through the hue integration app and the hue hub acts as a bridge to the devices that are connected to it.
In general its usually more cost effective to buy switches to control the lights for normal lighting and just use RGB in specific locations. Just remember that any smart bulbs you buy should have the switch left in the on position and controlled with triggers or automatons.
