Take a look at the sticky thread about Calibre-server. Here in
Post #125 I asked about running *JUST* calibre-server on WHS and the GUI on a client machine. KovidGoyal says it should work, since the server process will be Read-Only and the client will be Read-Write.
I think that will work for you as well - by pointing your GUI Calibre to the WHS directory for its library.
If you are *VERY* careful, you might be able to run the GUI on multiple machines - but like Ghostbusters, NEVER CROSS THE STREAMS
I would NOT recommend this myself though - as you must be 100% certain that only one machine has Calibre running at any time.
(There's another thread here which goes through that multi-client idea in excruciating detail.)
HTH,
Richard