Section 3 is alive and well. Congress cannot simply remove a section of an amendment - it would have to pass an additional amendment which would then need to be ratified by the states to take effect. Congress may, by a 2/3 vote, remove such disability from an individual, but Section 3 remains the law of the land to this day. See the below link to the U.S. Constitution from the Missouri Supreme Court website.

As far as being reunited goes, Congress obviously removed the disablitity from Confederate Veterans, since they served in Congress. As the last Confederate Veteran died in the 1950's, I would say this is a moot point overall. My favorite reunification/rivalry story is the Battle of the Ice Cream Truck between the old 69th New York and an old Alabama Guard as they were being merged into the 42nd "Rainbow" Division during WWI.