This mutator for UT4 adds vehicles, if the map is build with the Vehicle-MapKit for vehicle spawns.
This mutator is in prototype process, so bugs can occur. Hellbender is supported and more vehicles like Cicada or tank will be added. All coding is placed inside the vehicle, so other mods can use it.
Prototype Map: DM-RaceTrack
Forum thread: UTVehicle in Forum
Download the UTvehicleMapKit and place the Mutators folder in your Content folder.
Content > Mutators > UTVehicleMutator > etc
You can place the "Spawn" classes like "HellbenderSpawn" in your map. If you want, you can also use coding on the variables of the original vehicles. The coding is empty but the variables can be used.
You may want to use the mutator in your Level Blueprint:
Begin play > (get gamemode) Cast to UTGameMode > Set Mutator class (UTVehicleMutator)
If you see a map, where should be vehicles, you have to use this UTVehicleMutator as active mutator to spawn vehicles. The mutator will patch the map files for the vehicles. This allows easy patching and updating.
The most convinient way is to create own ruleset, category or gamemode tab.
If you are working on a big gamemode like Onslaught, it is possible to contact this mutator owner to send the whole UTVehiclemutator code over. This allows easy integrating into a gamemode.
-Keys getting detected. Jumping flips the car. Q or E enters/leaves the car.
-Hellbender is useable: 5000 Health, Respawn 5 seconds.
-Hellbender can smoke, explodes and has destroyed animation
-Driver can run other players over, gets kill and "RoadKill" voice (online)
-car respawn on expolded, KillZ or UTPain Volume overlap
Common mutator gamemodes 
- vehicle CTF (vCTF)