When talking about certification, one must remember that it is more about the journey than the destination.
The material one must master to achieve the VCP-DCV provides a solid understanding of the the vSphere infrastructure, which is the the only hypervisor with which NSX-v integrated. NSX-MH is available for other hypervisors, but there currently is no certification path for that product. I'd recommend a VCP-DCV first, depending on your job duties, but I know plenty of network folks progressing through the NSX certification track without issues.
VMware's courses on NSX, starting with Install, Configure, Manage, is what most folks seem to take as a start.
There are also great free resources available - the exam blueprint available from VMware, the documentation on VMware's site, Hands on labs, and the dozens of great blogs www.routetocloud.com, www.yet.org, networkinferno.net, bradhedlund.com