|Kemal at Gallipoli|
There also appear to be no records detailing the ethnicity of Ottoman conscripts. It is known that the Ottomans, even before the Arab Revolt broke out, preferred to station troops from the Arab provinces in Anatolia, the Caucasus, or European Turkey, and put ethnic Turks in Syria, Mesopotamia, and Arabia, for fairly obvious reasons. (Many were forcibly rounded up and were hardly serving willingly.) Though there were exceptions.
Some modern Turkish historians have begun to take an interest in this subject, but for decades it has been buried under Kemalist mythology: The Turkish Republic glorified the Turkish language and ethnicity, sometimes to ridiculous extremes (the "sun language" idea, claiming all languages descend from Turkish; or insisting on calling Turkey's Kurds "mountain Turks"). Mustafa Kemal began his rise up the high command ladder commanding the 19th Division at Gallipoli: after he became Kemal Atatürk, "Father Turk" himself, it was unthinkable to mention that his own division was two-thirds non-Turkish.
You might think that while Republican Turkey naturally dropped this fact down the memory hole, Arabs would have sought to preserve it. But not so. It did not fit with the mythology of Arab nationalism, either. The Great Arab Revolt was a universal Arab uprising against their Ottoman oppressors which (with maybe just a little help from the British) brought down the Ottoman Empire. Though this originated essentially as a Hashemite version of history, it became pretty general, and nobody was going to glorify Arabs in Ottoman service.
The Ottomans were proud of their multi-ethnic empire which, like Austria-Hungary's, was doomed to fall in that war, though from 1905 the "Young Turks" had been emphasizing Turkish ethnicity. Perhaps as many as a third of the Ottoman Army came from the Empire's Arab provinces, and right up to the Mudros Armistice there were more Arab troops in Ottoman uniform than the Arab Revolt could ever command, but their service fell victim to the dueling nationalisms of Turkish and Arab national myth, and so they were too inconvenient to be remembered.
The Arab role in the Ottoman Army has been a particular interest of Salim Tamari, the Palestinian historian, though his work is not focused on Gallipoli. His book Year of the Locust: A Soldier's Diary and the Erasure of Palestine's Ottoman Past (which I have not read) translates three war diaries, focusing on that of a private from Jerusalem (publisher's page here; Amazon link here; also see an article by Tamari in The Jerusalem Quarterly called "The Short Life of Private Ihsan: Jerusalem 1915"). For articles dealing more directly with Gallipoli, see Al Jazeera English, "The Forgotten Arabs of Gallipoli," and Robert Fisk in The Independent, "Great War Secrets of the Ottoman Arabs."
I intend to do more research on this subject, and will share what I learn.