Are bouncing projectiles possible?

Actually, yes.  The ground plane is the only collider in the scene that will work with Unity's Physics, so a rigid body attached to a projectile will actually work.

Just be aware that in doing this you'll be relying on Unity's physics system to simulate the bounce - so you could get inconsistent behaviour (as opposed to controlling the bounce yourself).  You'll also need to adjust the default Physics Gravity value to suit.