Can a Dependent use Space-A Unaccompanied in an Emergency?

If the emergency is for an immediate family member then according to DoDI 4515.13, Section 4, Table 3, Item 5 you should be eligible for CAT-I travel:  It states:  "Dependents, accompanied or unaccompanied, of members of the Uniformed Services who are assigned and domiciled in the CONUS" and travel would be authorised C-O (CONUS to overseas) and O-C (overseas to CONUS).  I only know of one person that has actually done it from BWI to Ramstein. You'd need a modified version of a dependent Space-A Letter from the Sponsor's commander.

In addition, you may be able for unit-funded travel (again, if it's immediate family) pe the Joint Federal Travel Reg (JFTR). I don't know the exact reference off-hand (I'd need to do some research).