No, you do not need to give your VA access to your seller central account.
The only time you would have to give them access to anything on your amazon personal account is when you want him/her to be able to check if products are hazmat or seller restrictions. If you do need him/her to check for these you create him/her a sub-account on Amazon Seller Central as well with very limited rights where they can only. Learn how to do this by
following this guide here.