If you want to do filtering (show/hide) of your views based on roles and privileges you can use the <privilege> tag inside the <metadata> tag of you extension.
If you want to really fetch the roles and privileges of a user from the vCenter the vSphere Client SDK does not provide this. Instead, please check if vSphere Web Services SDK (vim25.jar) will help - you can get more assistance on it on the vSphere Management SDK forum section.
Cheers,
Vladi