If the Platonic realm is to exist, can it be perceived if it is to be purely isolated by itself? Rephrased, how is the platonic realm perceived to be? Can it be imagined by itself without reference to the physical realm?
According to Plato, ideas are conceived only by intellectual intuition. Typical Platonic ideas are the beautiful, the true, the good, the just. Ideas strongly affect the objects of the perceptual world: An object is beautiful because it participates at the idea of the beautiful - according to Plato.
The clearest exposition of the ascent from the world of perceptual objects, i.e. our every-day world, to the realm of Platonic forms is described in Diotima's speech in Symposion, notably 210ff. In plain words, it is the process of continous abstraction.
The first harsh critique and rejection of the Platonic theory of Forms is due to Aristotle: Metaphysics, 990b ff. Aristotle started as a student of Plato at the Academy in Athens.
The answer to the question seems to depend on the perspective with which it is asked. First, from the perspective of a world where sensible objects never existed: Without an imperfectly beautiful object, we wouldn't be able to recollect the form of perfect beauty. The process of abstraction would never get started. So in this case, the answer is 'no'. Second, from the perspective of Plato: if we are talking about our world where sensible objects do exist, it seems that Plato would say that we can contemplate purely abstracted forms. In fact, he says that the person who escaped the cave would prefer to remain outside of the cave and contemplate the Ideas, rather than go back into the cave (516 c-e). So, the answer would be 'yes' in this case.