What do you mean by calling a DLL from one server to another??
You can create and Connect to dll's running on another server, but the dll has to be written to allow remote connections. The DLL must also be registered on the client machine before being able to run it.
The simplest way to achieve this if it is whats required is using Mictosoft transaction Server ( Component Services COM + ). The DLL is installed into MTS and then the client registers. When the client creats the objects, they are created on the server.
Vermix - Mapping a drive to the server will allow access to the DLL, but if you load it, it will be running on your client PC, Not on the server.
Hope this helps,
Chris Dukes