In order to get the phone into diagnostic mode, dial ##8778# and you'll see UART (MODEM, PDA) / USB (MODEM, PDA).

By default it's set for modem and then pda. To connect it to your computer in diagnostic mode choose modem for usb.

Remember to set this back to normal after done.

The drivers for the Epic or Fascinate work. Perhaps Samsung has some out for the Indulge specifically.