Legal Question in Real Estate Law in California

Maybe, maybe not. Depends on the easement and the agency terms/relationship.

There is no rule of law that automatically gives someone's agent the same rights, or for that matter, any rights whatsoever, in an easement. Determining whether Y can use X's easement across the land of Z requires a lot more factual information than merely knowing that Y is X's agent. The agency status may be relevant, or ma be irrelevant. Further, the answer may depend upon the purpose of the agency. X's agent to inspect the easement for safety and insurance purposes may have different rights that X's agent to market X's artwork.