Why not ask the vendor of the bluetooth module then? I can tell you where the connector is on the board, which you doubtless already know.
As far as the serial connection, I think the PCMCIA would give you a better chance at recognizing the device. I've also tried the USB to serial cables without luck.
Keep in mind that RS232 is an antique mode, typically not hot-swappable unlike USB, so a reboot may be in order whenever hooking up to your plotter.
Whether the card is...