Legal Question in Civil Litigation in California

Yes they can be served. In fact, they are required to be served unless the attorney agrees to accept service on that person's behalf through an acknowledgement of receipt.

If you're serving the summons and complaint (or plaintiff's claim in a small claims suit) after initiating a new lawsuit, then Mr. Roach is correct. If the lawsuit already has been filed and you're attempting to serve interrogatories, for example, then you should serve the attorney. More likely, though, you're talking about a new lawsuit.