As it stands right now, the material available to tourists at Gettysburg does not valorize the South - it is all about the fighting men, the generals and the units of both sides.
Gettysburg does not debate the causes of the war. It does not embrace the Confederate myth of a noble struggle for states' rights nor does it peddle the Union myth of a noble struggle against slavery.
What it does is document WHAT ACTUALLY HAPPENED ON JULY 2ND, 3RD AND 4TH 1863. Which units, led by which officers fought where and when in the battle. That's all. This business about the "High Watermark of the Confederacy" is not Southern propaganda. It is merely an observation that at the moment of Pickett's Charge at Gettysburg the South was at the absolute height of its military fortunes in the War and that after Pickett's Charge the military fortunes of the South began to decline. That's an objective historical fact, not a statement of partisanship.
Let the causes of the war be debated in the classroom. Let the actual concrete events of the battle be described as accurately as possible on the battlefield.