YOU need to specify to use pfSense as your DNS with the nslookup command otherwise it uses the client's default DNS config:
server 192.168.4.1
THEN try to lookup vcenter.smart.az:
nslookup
server 192.168.4.1
vcenter.smart.az
What does it come back with?
What is the contents of your Linux client's /etc/resolv.conf file?
Acutally, it doesn't matter if you enter fqdn or ip address in nslookup, it should resolve both.
You are trying to resolve hostnames to IP addresses. That was your stated problem. Doing a reverse lookup doesn't help you with that.