Yes, it would be surprising if even a third of those fighting Assad in Idleb are ethnic Syrians.
I had not heard of this group before.
The Imam Bukhari Jamaat (Uzbek: Imom Buxoriy Katibasi, also Katibat Imam al Bukhari) is an Islamist Salafi group fighting in the Syrian Civil War and the War in Afghanistan, composed of primarily Uzbeks, and expressing loyalty to the Taliban movement. The group originally operated only in Syria, where it is allied with other jihadist organisations such as al-Nusra Front and Ahrar ash-Sham, and alongside these other groups it makes up the Army of Conquest, which overran much of Idleb province in north Syria in 2015. Since late 2016, the group has also began to fight against Afghan National Security Forces, and has claimed to have set up training camps in northern Afghanistan.
So what will be done with the Uzbeks/Uyghers/Chechens/Turks
when the “Civil” war is over?