There is nothing at all wrong with honoring leaders of the CSA, as a reflection of the history and culture of the South, but revering them as "American" heroes is another matter. If the Army War College posted portraits of Lee and others in admiration of their leadership and soldierly abilities, that of course makes sense (if you ever have the chance to visit the US Military Academy at West Point, there are statues of some of the great generals in human history in the Board Room (I don't recall what the official name of this room is, where the Superintendent presides over the Academy leadership) but this is not acclaiming them as anything more than that, i.e., their military greatness. If the Army War College's intention is displaying portraits of generals who were heroes to this county's conflicts, then there is no place for Lee, Jackson, Longstreet or any of the others who fought against the Union.
You will not find, in a similar vein, any monuments to Benedict Arnold at West Point or in Washington, D.C. despite the fact that he was a hero early in the Revolution. Once he became a traitor to the cause, and served the British, he no longer deserved the honor of being considered an American hero.