All fonts are allowed.
Add the following line to your exp bar file:
Code:
<TextStyle Algorithm="Simple" FontName="FixedSys" Language="english" Name="FixedSys12" PointSize="12" UseCachedFont="true"/>
Just replace the FontName "FixedSys" with the name of the font you want to use. (Courier New, Symbol, whatever.)
Then have your text objects reference the Name of your font ("FixedSys12" in this example) instead of "/Fonts.FontZapf15" or whatever they currently use.