Hi,
You can rotate the tilemap so it is on the XZ plane if you want, but you can also make your game on the default XY plane and then rotate the camera to compensate. You'd need your own character controllers to move as you'd expect in a 2D top down (without gravity) game, but apart from that - 2D toolkit tilemap just generates tilemaps + edge collision shapes, you can do what you want with it.