Yes, Universal Naming Convention (UNC) pathnames can be used instead of mapped drives when you have ArcIMS components on more than one computer. In fact, if the output directory for images generated by the Spatial Server resides on a different computer than the Web server, UNC paths are recommended since one drawback to mapped drives is that they are inaccessible if no users are logged in to the computer with the mapped drives. UNC pathnames will continue to work in this situation.
A sample UNC pathname is //myserver/output.
Below is a portion of an ArcIMS 4.0.1 aimsdefaults.properties file using UNC pathnames. Earlier versions of ArcIMS may not contain all properties shown here.
#Thu Dec 12 17:07:49 PST 2002
The Website directory needs to use an absolute pathname.
Whenever possible, reference local drives directly (i.e., not using UNC or mapped drives). Using UNCs may be slower than accessing local drives directly.