You would have to research and follow your specific state laws, or those state laws you are working in for a specific answer. I use an extensive release that I got from Scott M. (on this forum) that works in most cases, but not in all. Everything depends on the state and it's interpretation of the forms you get signed for the information you request.

Release forms: Forms willingly and voluntarily signed by all parties to the bail bond contract. They vary in content and purpose, some are even governed by state law, but genreally, yes, they are basically limited powers of attorneys the client signs as a part of the contract.

GPS devices: Again, 1) Everything depends on local laws. 2) GPS records are not always admissable in court.
3) You have to have visual confirmation that the def is the one physically driving the vehicle.
4) Crossing jurisdictions: GPS unit may be legal in 1 area, and not in another. Therefore any information gleaned from an illegal acitivity may negate the apprehension and get you sued or arrested or both.
5) Covert deployment: If you deploy a unit on a def's vehicle, or whatever vehicle is connected to the case, and you don't have permission to do so, then you could face criminal charges as well.

Now, if the def gives you written consent to deploy a tracking device then you have no legal issues. This then falls under a different category called "Defendant Monitoring". Some bail companies actually do require thier higher dollar bonds to agree to wearing these devices as a conditon of thier pre-trial release contract.