I don't think the reapers were mindless, there was different individuals and they did directly speak to you at various points in the trilogy be it soverign or harbringer.

However on second thought there could be some interesting ways to indirectly use them to one's own ends if they're a unthinking force of nature.  If their creators are still alive, they might have some personality through them anyways (like what the hell is going through their heads to justify making a galaxy wiping weapon).  It seems I got too caught up thinking of them as a civilization as opposed to a organic berserker drone force.

Like using them as a weapon for your own ends or something like that.

But I still wonder why they are needed if their only purpose is to invade darkspleen's civ.  I

Wait...

What if darkspleen's civ is the creators?!