Yes you a helmet is required. Why would you want to ride without one any way?
Hello fellow smokster, even in some states is not mandatory wear a helmet, drink in your head, ALWAYS BRINGS HEADGEAR, is my advice.
It is my impression that the Spyder is classified as a motorcycle even though a motorcycle endorsement on your license is not required (just like a sidecar rig), wearing a helmet is required. I am not sure what the requirement for parking the Spyder is. Normally a motorcycle is parked crossways in a parking space with the rear wheel touching the curb. I don't think that is practical with a Spyder because of its length. I believe that being classified as a motorcycle allows that Spyder to use the HOV lanes with only one person aboard. The current DMV document can be found here http://www.dmv.ca.gov/pubs/dl655/dl665mcycle.pdf.