You are right: In order to model whether a transmission from a car to a certain "point" in the simulation is received, you will need to instantiate an OMNeT++ module (let's call it a Virtual Induction Loop, VIL) with an 802.11p radio at that position.
A design decision will be how to estimate where these VILs will need to be.
Naturally, VILs will need to be close to the lanes that are controlled by traffic lights. Each traffic light can control any number of intersections, so putting a VIL at the center of "the intersection" will likely not be possible. This means that, ideally, you would hand-pick the positions.
Alternatively, you can try to estimate a good position automatically. As of Veins 4a2, only rudimentary commands for traffic lights (such as to set a traffic light program) are implemented. SUMO, however, offers many more commands for reading traffic light information. If you implement the commands to enumerate which traffic lights exist, which lanes they control, and where those lanes are, you might be able to derive good position estimates for the VILs.