gnetlist Cannot Find Symbol
I found the answer to this by looking at the gnetlist log files in ~/.gEDA/logs. The problem was that I had some things in my gafrc file that were valid for gschem but were not for gnetlist. As a result gnetlist was apparently not loading the rest of the file where the component-library command was. Once I removed the gschem-only commands, gnetlist was able to load the symbol and complete without any warnings. The subcircuit components were then in the output netlist as expected.