Do I need to run DNS on a colo server being accessed remotely via VPN?

Question

My Mac Mini Server is located in a colo site. We generally use it for Web, email and a couple of application-specific services. It has a dedicated IP address. We have a separate DNS service we use to point to the domains on the server located remotely from the server. Forward and reverse lookups work fine from the server, even though the local DNS service is turned off.
However, we now have a couple of things we want to access remotely on the server via VPN (for example, some files via AFP). The firewall blocks remote AFP requests (using the built-in firewall, not a separate box). We can connect via VPN without problems. However, AFP does not work. If I allow AFP in the firewall and try to connect, no problems at all.
Since the Mini is located by itself and will never likely have anything connected to a "local network" (never running DHCP, etc.), there generally doesn't seem to be a need to run DNS on the server.
I suspect the problem is that when you VPN into the server you are on its "local network", whatever that means, so the DNS does not resolve since the local DNS service is not running. However, I am not positive of this.
Must we run local DNS? Does it have to mirror the remote DNS that we currently reference? Can we somehow "reference" the local DNS from VPN clients trying to access local services?
I hope this question makes some sense.

Answer 1

Bear with me please....
The Mac Mini is in a data center on a shelf, getting a direct connection to the Internet via ethernet with a fixed IP address (under the covers, I suspect that the data center is using some sort of router or switch, but I am not paying for a hardware firewall or other gateway). There is no local network for the Mini. It is not running DHCP, not handing out NAT addresses, etc. DNS is currently off. Rather than using the local DNS, the Mini is resolving its DNS needs with a DNS server located at another site, over the Internet. This seems to work fine (i.e., changeip confirms it is working and services seem to work).
I am currently using the software firewall built into SLS.
I want to turn on VPN so that remotely located computers can access services on the Mini without having to make the services visible through the firewall.
I am able to connect devices via VPN with little difficulty (iPhones, Macs, etc.). However, when I try to access services (let's use AFP as an example), I cannot access them UNLESS they are allowed through the firewall. This tells me that I am not seeing the services through the VPN, but rather through the Internet directly.
What I meant by "local network" is that the VPN allocates local IP addresses when devices log into the VPN service (10.0.x.x). There is no DHCP allocating these addresses, just VPN.
My question is: why can I not see the services on the Mini blocked by the firewall when successfully logged into VPN on the server? Isn't the whole point of the VPN to gain access to services behind the firewall?
I am guessing (with no particular information to support my thesis) that somehow without DNS running on the Mini, VPN clients are unable to access services on the Mini. I do not know for sure, however, if this is the problem. If it IS a problem, then the question is whether I should completely copy the DNS entries from the remote DNS server to the Mini and start the service. Will that solve the issue? Create conflicts with the DNS (since it is now located on both a remote service and on the Mini)? It certainly will create a maintenance headache since now I will have to maintain the DNS in both places.
I am hesitant to migrate all of my DNS services to the Mini (because I will also have to go to the domain registrars to change where they point, etc.) to eliminate the remote one. And I am not sure it will solve this problem anyway.
Sorry for all of the typing!