Can you write-protect DFMA libraries in a network location, so that multiple users can use the same library data?

Yes. These instructions apply only to DFA and DFM Concurrent Costing. Users of other BDI applications should contact Support at BDI. End users should set the path to the network library in the Librarian dialog (Tools menu.) They will be able to add and use data from write-protected library files in performing analyses. If they open the library window, they will have the opportunity to work with a copy of the library, but will not be able to make changes to the library stored on the network.

See the FAQ What are libraries in DFMA software? for a definition of a library.