Recently there is a separate specific NSX and vSAN vExpert. So if you are focusing on vSAN or NSX, do sign them up here respectively; vSAN and NSX.
If you are unsure whether you meet to be accredited with vExpert, there is no harm trying. The details of the area you can be in are all listed in the vExpert 2017 sign up page above.
While you are reading this, the top vBlog 2017 voting has started. Do help do your part and vote. If you find my blog useful spare some time and look at number 88.
Once again thank you and good luck for your application.