In a three-way circuit does every switch need to be a dimmer, or can the switches (not connected to a load) be relays, if I want to be able to have dimmer functionality. just wondering since the relays are cheaper than the dimmers.
Only the switch that actually is connected to the load needs to be a dimmer. Any switch, even a relay device, can be used to dim and bright on dimmers it is controlling.
Does the relay switch have the full range of LEDs and do they respond accordingly?
No, there are fewer LEDs on a relay device and they reflect the status of the built-in relay--on or off only. That, and the fact that relay devices make a slight "click" when they turn on and off means my first preference is to use a SwitchLinc Dimmer as a 'slave' in a multi-way dimmer setup.
That said, there may be times when you are building a multi-device scene that controls both dimmable and non-dimmable devices. In that event, be confident that you *can* use the relay device to adjust the dim level of linked dimmer responder devices or the speed of a fan.