Only if they could find the OBD port, and you make it easy to remove the plug in tracker- I know it's not easy to hide a blooming great plug on a bundle of wires...you have to be creative and make it as difficult as you can for someone to get access.The OBD Tracker that you mentioned earlier seems like a good idea but I would imagine that thieves would remove this if they were successful in stealing the car? There again, perhaps some wouldn’t?
By the time they realise it has one fitted, you may (if it's a good system) already know where the car is.
Only by trial and error - there is no known cure for the hanging session issue.You said that.....“it may be found that the OBD port powering the tracker may hang the ignition shutdown routine - this will be a trial and error exercise.” Can this easily be sorted out?
There are many trackers, the best seem to be subscription devices that use the mobile network. Follow the advice of expensive plant operators that use specific devices for assets that are worth far more than our cars.
I'm not going to recommend any such device for obvious reasons, but your'e on the right track.