yeah but when used in a car, you have to keep an eye on your phone AND bluetooth puck's battery levels.
On long trips, I used to switch between which device was getting juice from the car's power (have one usb charger).
My battery life has been so much better ever since internal GPS is enabled, since now I dedicate all my car charger time to the mogul!
If battery life is your reason to use a BT GPS puck, I'd say get a spare battery for the mogul and just use one device.
Better signal I hear, but to be honest I don't get that much faster of a fix with my holux.
To answer the OP, no, a bluetooth puck by itself can't be used as a tracking device since its not actually processing the information. Its simply pulling the info from the satellites, doing some quick math, and sending raw data to your phne/PDA/laptop/whatever to interpret your location on a map. There is no memory or sophisticated CPU on these things to run your own application or store the data.
If, however, you have an old PDA with bluetooth (ipaq 1940 anyone?), you can strap it to the back, run GPS trailing software, and drop the whole thing in someone's bag as a tracking device. But once again, wihtout something to connect to, its pretty useless.