Yes. It's currently the latest that's been published and the API should be backward compatible. Sony said they are working on a new Script SDK package to document some of the changes they have made with Vegas Pro 13.0 but it hasn't been released yet so the Vegas Pro 10.0 SDK should be fine to get you started.
JR is right. The changes from v10 to v13 are quite small, so if you start with the v10 SDK, you'll be 99% there. Keep an eye on this forum -- I'll post a link when I get the v13 SDK ready for download. I predict sometime in May, but please don't hold me to that date! It's just a guess.