If theives wants to steal something, they're going to get it. Most of what anti-theft systems do is make the situation less attractive so the thieves hit some other target. Tracking helps with recovery, to be sure, but is only as effective as a thief's unawareness of it.
Given how much depends on GPS it'd be unlikely for more theft situations to involve blocking it. Turning off equipment, sure, but outright blocking of the radio signals through jamming is going to bring wider attention much too quickly to be useful. Anything's possible, of course, but very little is actually likely.
I think it's fair to say that if you want theft recovery based on GPS coordinates and uplink signals you're going to want to go with something designed for the purpose AND properly installed in a concealed manner. AIS using your boat's GPS and chartplotter system is probably not it.
-- Bill Kearney
2005 Eastbay 47 FB - Solstice, w/Highfield CL360 tender