Hi Teargas (nice name! ;-)
Understand that for a native VST Host the Jacobi.Vst.Samples.Delay.dll is the plugin. It is in fact the Jacobi.Vst.Interop renamed to mach the name of the plugin. The .net.vstdll file contains the managed code of the plugin itself. So try pointing the host
to the dll file instead of the .net.vstdll file.
Further, you don't have to put the Core and Framework assemblies in the GAC. Just put them next to the the other plugin files.
Also some hosts require you to manually refresh the plugin cache. Look for an option called "rescan" or something similar.
Start with VstHost.exe because that is the same host I use for testing. Add the plugin by browsing to the .dll file. If it still doesn't work, please provide a detailed report of your actions.
So hang in there, we will get it working ;-)
Hope it helps.