My DataSnap appserver is now instrumented. In fact, my performance counter libraries are generic and will work with all DataSnap servers installed on the computer. DataSnap class IDs are read from the registry and a separate performance object instance is created per each class ID.
I have created two performance counter DLLs, one for web (httpsrvr.dll) and another for socket (scktsrvr.exe) transport.
I'm looking forward to watching the graphs later this month; some serious load is expected on our website when the users are back from their vacations.
Links to the source code:
Custom Performance Counters
Performance counter libraries for DataSnap appservers