Click on the link below and scroll down to page 32-35 for more information. In California they do everything on a case by case basis and will not give anyone an absolute answer until they make their final decision based on everything you submit with your application. I am not sure if this is the latest info but the basic guidelines are the same, it is hard to find certain info on the website. The rest of this document explains all the different possibilities of losing your license, probation, rehab, suspension, etc. They use these same guidelines when making decisions on initial applicants as well, not just those who have done something after they have their license. It might be good to read just to be familiar with how CA BON works. http://www.rn.ca.gov/pdfs/enforcement/discguide.pdf
One thing is to make sure you submit as much info as possible, especially regarding attempts of rehabilitation. And yes, dismissal (expungement) will help even though it still shows up on your background check. The BON sees it as your attempt to do whatever you can to be responsible and make it right.