It is has been a while since I did something with arduinoBT. So, answers may not be accurate. If you have some patience, I plan to pick it up again in 1 or 2 weeks or so.
according to the iWrap manual, this disables the escape sequence and sets the wt11 to command mode when the PIO0 goes low. I can't see a PIO0 on the schematic http://www.arduino.cc/en/uploads/Main/arduino_bt06.pdf and no wiring to any of the GPIO pins.
You have to pick up the GPIO pins next to the WT11. There are through holes, you have solder some wires in them.
- is it possible to use a different SET CONTROL ESCAPE command in my sketch to enable the +++ esacpe sequence? I'm concerned that doing so will make the communication to the PC stop and I'd then have an unusable Arduino;
No, changing the escape sequence will not render the arduino useless.
- is using a hardwired link to one of the wt-11 PIO pins preferable?
Well, that depends on what you want to do with it. But if I am not mistaken the firmware on the WT11 is too old for this to work. You have flash it with a more recent version. If you have the escape sequence working you can query the WT11 to see what version it is. I ordered my BT board immediately when it was available, maybe the firmware on the more recent boards is uptodate.
I would advise to read the bluegiga documentation a few times, the firmware and user guide. Play around with the code from the first thread you mentioned.
Do you have a specific project in mind?