Visiting the graves of the martyrs of Uhud is مستحب as part of the general السنة of visiting graves. النبي (صلى الله عليه وسلم) himself visited the martyrs of Uhud, made دعاء for them, and said his farewell to them. Hamzah ibn Abdil-Muttalib, النبي's uncle and the 'Lion of Allah,' is among those buried there, along with approximately seventy other companions who fell in the Battle of Uhud.
الشيخ ابن باز stated that visiting the martyrs of Uhud follows the same etiquette as visiting any graveyard: the visitor greets the deceased with the السنة greeting, makes دعاء for them, and reflects on death and sacrifice for the sake of Allah. The visit is a beautiful reminder of the sacrifices made by the companions and the meaning of steadfastness in faith.
However, الشيخ ابن باز also warned against several practices that have no basis in the السنة: climbing Mount Uhud as a ritual, touching or rubbing the mountain seeking blessings, taking stones or soil from Uhud as 'blessed objects,' making دعاء to the martyrs (rather than for them), or considering the visit an واجب part of the الحج or العمرة trip. The visit to Uhud is voluntary and falls under the general recommendation to visit graves. It is not connected to the rites of الحج or العمرة in any way.