I am in California and observe at traffic trials a lot. While I don't pay particular attention to carpool tickets, I recall hearing judges tell people with tickets for driving in the carpool lane that there is no point attached and so they are not eligible for traffic school. I have noticed, however, that tickets for crossing the double doubles to get into or out of the carpool lane DO carry a point.
So, you should research this one some more. One place you will definitely want to call (anonymously, or or a "hypothetical basis") is your insurance company. Ask them what their reaction would be if you got a carpool ticket on your record.
NACOL