Hello, yes, this should be possible, it is the same thing as if you would protect a folder on an external volume.
The only limitation is that the folder can be unlocked only from one Espionage at a time, and I'm not sure how can you control this if you have multiuser access. Relying on users to "promise" they will not unlock the folder if somebody else is using it, is not reliable. Also, it is not possible to see from another Espionage installation if the folder is already unlocked or not.
So, if you can make sure that only one users uses it, then we can move on, if not, then this will be the main problem.
other then that, they way it should be set up is the following: you protect a folder from the first installation of espionage. once the encryption is done, click onto small "i" near the folder name and with disk image drop down menu select the location of the disk image, probably the folder on the file server. On the same screen, click on the copy password button, and paste the disk image password into a text file you will access later from other macs for further setup.
now go to the other mac install espionage, create a local empty folder, locate the disk image on the file server and drag it to espionage, it will ask you for password, use the one you saved into the text file, then it will ask you for mountpoint folder, select the local empty folder you just created.
repeat this on every mac you want to have access this folder to.
let me know if you have any further questions
rgds
Zsolt