As I can imagine, "simplified arabic" is not particular font, but a font family. So it relies on font substitution logic - to auto-find a font has simplified arabic glyphs.
It is difficult to say why it does not work in your case. I would try to explicitly define the font family in pd4fonts.properties and assign to it any TTF, which has the Arabic glyphs. For example:
simplified\ arabic\ Bold=arialbd.ttf
simplified\ arabic\ Bold\ Italic=arialbi.ttf
simplified\ arabic\ Italic=ariali.ttf
(and make sure, the mentioned .TTF files are available)