May the registered owner of the vehicle be held liable for damages suffered by a third person in the course of the operation of the vehicle?

Yes. The registered owner of a public service vehicle is responsible for damages that may arise from consequences incident to its operation or that may be caused to any of the passengers therein (Gelisan v. Alday, G.R. No. L-30212, Sept 30, 1987). Also, the liability of the registered owner of a public service vehicle for damages arising from the tortious acts of the driver is primary, direct, and joint and several or solidary with the driver. (Philtranco Service Enterprises, Inc. v. CA, G.R. No. 120553)