If you want to use lower layers of Veins, you will need to write an adapter module yourself. Its design is straightforward: to upper layers, it will look like an INET NIC, to lower layers it will act like a Veins application.
Note, however, that recent versions of the INET Framework offer an easier way: their WLAN NIC can be configured to behave according to 802.11p. While this has not received as much use as the modules of Veins, it should serve as a reasonably-safe alternative in many applications.
See the veins_inet
example of recent Veins versions for how to configure INET to model 802.11p VANETs and, at the same time, use Veins for ensuring realistic road traffic.