Can vehicles be added easily in any module made for game creator?
Sure. Here's a video explaining how to do it.
However, this video is a bit outdated and now it's much more easy to do. There's an Action called "Mount" that takes care of disabling all control on the character and any collisions, so the character can safely enter any vehicle (although you'll need to provide the animations) and let the vehicle control how the mount and the character move.
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