Is there a realm outside the mandala?

The Buddhist circle or sphere of influence, is particular to the three jewels. In the unformed and more realised spheres, the division between a mandala and for example a tariqa is non existent.

Is the Mandala a Hindu teaching?

Teachings associated with Brahmanic religions, use the idea of a wheel to organise realms of thought. In other systems a more hierarchical tree and branch or pyramid structure is used.

Can the mandala be used as a psychological tool?

Any system of division is a memetic way of illustrating opposing or potentially complimentary attributes. Superficial, new age and fad based pop psychology often finds a use amongst the crystals and tibetan singing bowls.