Yes.. Lojack in the DR is under the US corp. bounds.
The only thing is that they may require that you pay an extra fee to have DR coverage for theft while here...
LoJack have an office on Ave. 27 in between Churchill and Nu?ez De Caceres.
They also have an offer running with Seguros Popular, costs around US$350 to be installed etc.
I am not sure in DR but in the US it is a one time fee. You have two options: the standard tracking when the vehicle is stolen and, the active warning system that lets you know (and Lojack) if someone is stealing your car.