On a 4-way light system can just one of the 3-way or 4-way switches be replaced with a 3-way or 4-way dimmer switch to dim the lights that will maintain the setting of dimness when the other switches are turned on? Just one master dimmer that maintains its setting regardless of which switch turn on the lights.
For standard switches, that is true. Only one of the switches can be a dimmer (it needs to be a 3-way type) and the other switches are conventional on/off 3- way and 4-way switches. Each of the non-dimming switches turn the lights on at the level set by the dimmer switch. But to change level, you need to go to the dimmer.
There are more sophisticated systems that use a master and slaves. In these systems, each switch can turn on and off the lights at a preset level, or they can override that setting and each control brightness. These switches need to be a matched set, require neutral wires as well as hot, and cost a good bit more than conventional.