Can I use my own DNS server
Yes, you can.
By default, a DNS program is active on a VPN server. It is used for resolving DNS requests from the VPN connected devices. It helps to make sure that the DNS is not leaked when the VPN is connected.
But in some cases (mostly for business use cases) you may need to force your users to use your own DNS servers while connected to the VPN. It is possible to use external DNS server with a UTunnel server. In such cases, all DNS requests will be sent to the external DNS server when the VPN connection is active on a device.
Check how to enable external DNS on UTunnel server