From a JDB suit against me, the evidence they had on the summons was an affidavit from someone from their company (not the OC) saying they had knowledge, etc. I did file a motion to strike the affidavit, but it will not even be read until we go to court.
When I received my notice to go to court, there was a part about if I wanted to have a witness summoned to contact the clerk of the court. I called and was told that I would need to come down to fill out the paperwork and would need the name and address of the person.