Can you use VPN and DNS Firewall together?

Yes, VPN vs Firewall are not conflicting entities. VPN Unlimited perfectly complements DNS Firewall. VPNs are like an additional IP stack on your system, which means that you can have a separate DNS server address configured. However, this is only possible if the VPN is made for this. So, if you use VPN Unlimited with DNS Firewall, this will work perfectly.