There are only a few vehicles you can add a logo to, like the covered 5th truck. Place the truck on your map (make sure your "logo" is in your mission folder). and in the trucks init field put...........
this setobjecttexture [0, "NAMEOFPICHERE.jpg"]
The maximum size of the pic is 512x512
Hope this is what yer needing, if you use the OX2 Lite, remember that it will be like a "NEW" Addon and all will have to DL it.