Can I Select to Report on Multiple Dimension Values at the Same Time?

Martus reporting is very hierarchical. Specifying a parent dimension value will always include that parent and all of its children.  

There is no way to select multiple dimension values from within a single dropdown. 

However, you can set up a separate user profile with access to the group of departments (or other dimensions) in question to see a consolidated view.  See this Knowledge Base article for information about setting up user profiles.