Yes, the 5th Alabama Infantry fought in the battle of Gettysburg, but Major Blackford of the 5th Alabama was detailed to lead a separate and distinct unit of sharpshooters. Yancey's 17th and Stallworth's 23rd Alabama Battalions were organized commands with field, staff and company officers; Blackford's was not. I believe Capt. Moreland's sharpshooters of Cantey's brigade was another ad hoc unit, but have no definite evidence on that.

Sometimes we see such organizations as separate and distinct commands, such as Yancey's Sharpshooters which served with Deas' brigade in the Army of Tennessee, or the 2nd Georgia S.S. Battalion, which served with Jackson's Brigade of the same army. Later (1863) we see ad hoc units of detailed men like Blackford's at the division level. General Cleburne had a small corps of sharpshooters which served with his division.

As an aside, the ordnance officer of Wilcox's Alabama Brigade received (and presumably issued) two Whitworth rifles and equipment, including bullet molds, on June 30, 1863. I'd have to assume that these were issued to men assigned to duty as sharpshooters with Anderson's Division. Any other information on that?