According to the documentation, otf fonts are acceptable, and there are already many of this type of font listed as being registered on the server as well.
However, I get an error when I try to register a new otf:
Unable to add font 'C:\Windows\Fonts\AauxProOT-Regular.otf'. Your path must be a valid absolute path. Acceptable paths are:
C:\myfonts\ C:\myfonts\tahoma.ttf
C:\myfonts\gulim.ttc
/opt/myfonts/
/opt/myfonts/tahoma.ttf
/opt/myfonts/gulim.ttc
Acceptable font extensions are:
TTF (True Type Font)
TTC (True Type Collection)
AFM (Adobe Font Metrics)