Should dark matter play an important role in designing a quantum theory of gravity? Since dark matter "accounts" for most of the matter of the universe, and its effect are inferred from the gravitational effects, should it play an important role in designing an unified theory between quantum mechanics and gravitation? I mean, is dark matter all about gravity or do we, somehow, have to use quantum mechanics in explaining it?
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Since dark matter "accounts" for most of the matter of the universe, and its effect are inferred from the gravitational effects, should it play an important role in designing an unified theory between quantum mechanics and gravitation?

Quantization of gravity is an open research question. At the moment models based on  string theory are known to include quantization of gravity, except no definitive model has been selected out of the enormous number of possibilities offered by the theories. If one assumes that a definite string theoretical model will become the theory of everything (TOE) then the existence of dark matter is independent of the quantization scheme for gravity.

I mean, is dark matter all about gravity or do we, somehow, have to use quantum mechanics in explaining it?

It is expected that weakly interacting particles from an extension  (into  string theory) of the standard model of particle physics will be forming the dark matter part of the universe. These, in the macroscopic dimensions of the galaxies,  will behave as all other matter, except not interacting with the electromagnetic field.
If in the future a more promising theory of everything appears not based on string theories , it might be that dark matter will be a different story. Currently mainstream physics is waiting for results from the LHC experiments to see whether the scenario of new weakly interacting particles will materialize.
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Should dark matter play an important role in designing a quantum theory of gravity?

No. The thing to appreciate about quantum field theory is that is that virtual photons aren't short-lived real photons that pop in and out of existence. Instead they "only exist in the maths of the model". They're field quanta. It's like you divide an electromagnetic field into arbitrary abstract chunks and say each is a virtual photon. Then when the electron and the proton attract one another, they exchange field, such that the resultant hydrogen atom doesn't have much of an electromagnetic field left. You can see from this that the exchange concept makes sense. QED "works", but hydrogen atoms don't twinkle. 

Since dark matter "accounts" for most of the matter of the universe

We don't know that. People refer to "dark matter" to account for gravitational anomalies such as flat galactic rotation curves. But we don't have any evidence to say it consists of actual matter. And see what Einstein said in The Foundation of the General Theory of Relativity: "the energy of the gravitational field shall act gravitatively in the same way as any other kind of energy". A gravitational field is a region of space where the energy-density is higher than normal. This spatial energy has a mass equivalence and a gravitational effect, but it isn't made of particles. It isn't matter. That's not to say "dark matter" is spatial energy, but it should be enough to demonstrate that it needn't necessarily be matter.  

should it play an important role in designing an unified theory between quantum mechanics and gravitation? I mean, is dark matter all about gravity or do we, somehow, have to use quantum mechanics in explaining it?

I can't see how dark matter has any role to play. And I'm afraid I can't see how the exchange concept has any role to play either. Because when two hydrogen atoms attract each other gravitationally, they don't exchange field. Instead the two fields are additive. So the exchange concept doesn't fly. It just doesn't "work" for gravity.   
