I had the same problem when experimenting with Chinese fonts. I finally managed to get it working.
What I did was, when I open my .TXT file in Word, I select an encoding which CAN read the font (not UTF-8 - which as you discovered, garbles up the text) and then save this file into PDF (instead of RTF). And from this PDF, I convert it into .MOBI (I use Mobipocket Creater).
This works for me and I hope you get it working as well.