If the command to the plug-in is triggered from server A on the application on server A.
I don't think it will work when the plug-in is triggered from server B to act on an application on server A.
But I don't have thát deep experience with that kind of separation.
Usually I split my application in separate files, one of which is web access.
File references in 7.0 and later would allow, even encourage direct access to the same tables, regardless of which file they reside in. Don't know if it is the same for different servers....
Some of the work that developers have been involved in is separating the layouts, logic, scripts in one file, a file which has no tables and having the data in a file which only has tables and data (no layouts, scripts, etc.). There are several advantages to this architecture, ease of updating databases is one notion. Creating only one file for access to web is probably prudent and a simple way of controlling access to data. It would also provide a tight structure and architecture for IWP.
If you can achieve the same with separate servers...I don't know...