Absolutely, if you go into your namecheap panel and click on a domain under "Advanced Options" on the left side you will see "Nameserver registration" from there you add in your root ip address from your VPS (19X.XX.XXX.XXX) in the boxes for NS1 and NS2 with your domain. Click save and then go to "Domain Server Setup" under the general category, and in there enter your NS1.DOMAIN.XXX that you setup in the last step, do this for NS1 and NS2.
When you setup the domain in Zpanel it should have automagically setup your DNS entries already as NS1.DOMAIN.XXX for NS1 and NS2, but if not then Go into the "DNS Manager" in Zpanel, choose your domain and then ensure that the settings in "A" for NS1 and NS2 show your IP address(es) and on the NS tabe that is has n1.DOMAIN.xxx and ns2.Domain.xxx in the targe fields (@) should be in the hostname field.
For subdomains they are setup to automatically point to that same name server, meaning that to my knowledge you cannot have car.domain.com pointing to a different Name server tham domain.com, BUT you can certainly create its own file structure and database if you choose to do so for instance with forum.domain.com you may want a forum rather than a wordpress setup in domain.com (or whatever you choose to use.)
Zpanel took a while for me to get the hang of, but it's really pretty good, I found as well that sometimes you may need to reboot your machine to get the DNS to work correctly, this has only happened to me once, but a simple "Sudo reboot" fixed it up just fine, and since the box boots up so quickly it's no big deal to me.
Okay that is how I had my namecheap settings setup since yesterday, but I'm not sure on the zpanel. This is what I have in zpanel: https://dl.dropbox.com/u/40710/DNS.PNG
Is it correct? Notice that NS1 has the first IP and NS2 has the second IP. Is that correct?