I think if objective truth exists it must be what exists regardless of our perceptions. According to QP, there is not a clear line between our perceptions and outside existence, though we can safely assume that there is an outside existence. This outside thing would be objective truth.
Now, as to your second question, I do not really know if it is attainable or not. Certainly our minds in their normal state could not see existence clearly. We percieve things at a conceptual level, and at this level, we can only give meaning to things by their opposite (beauty only means anything when compared with ugliness, an object's front is only definable by defining it's back (which ironically can only be defined by first defining a front)). At this level, no, I do not believe we can 'see' objective truth. If we stop seeing things semantically, it might be possible, but at that level, no concepts can exist, thus once one is in this state he no longer has an intellectual 'understanding' of the truth, just an awareness of it. Because of this it would be more or less impossible to communicate this truth using words or books, etc. because these rely on semantic thought. This is the basic buddhist/hindu/taoist train of thought.