I tried this and it didn't go so well. But I didn't do the collision model and the high poly car model kept eating my car when I collided (probably front facing normals or over-detailed model) My advice would be to import it into Blender, then make a simplified version for the collisions, then export (making sure to follow Beamng's very specific file structure) as a .dae. Should work, but the textures will be a pain, as you'll likely have to manually sort them out.
this works hooray!! for those who also want a ramp and are trying to do this but cant, make a copy of the an12ramp folder, or t=just the whole mod itself, then go do the mod, and go to "an12/vehicles/an12ramp " and paste the ramp.jbeam file i put here, which will replace the original ramp.jbeam. i gotta thank this guy a million, can believe i hadn't replied sooner, i totally forgot