Don't know about local militias but I can tell you plenty of interesting stuff about the balkan people's involvement with the Ottomans. I know many
Bosniaks helped the Ottomans during the gallipoli campaign.
But to go back further, and by that I mean when the Ottoman Empire was still new. Obviously many Orthodox nations in the balkans were ottoman vassals, and they helped us out in plenty of wars. Serbs stand out in particular, in two cases. First in 1402 Battle of Ankara, and second during the 1453 Fall of Constantinople.
There was a war that nearly destroyed the Ottomans during 1402, between Timur's Empire and our empire, it was a crushing defeat where the sultan himself would fall captive. Serbians were Ottoman vassals during this time and as such, they helped us out during the battle. Stefan Lazarevic, the Serbian prince himself fought in it. At the Battle of Ankara, the only Ottoman forces that conducted themselves in an exemplary fashion were the Serbs. Stefan Lazarević and his knights together with Wallachian forces successfully fought off the Timurid assaults and cut through the Timurid ranks three times. Each time Stefan advised Bayezid (the Ottoman sultan) to break out with him, Bayezid declined to do so. But the Serbians managed to save one of Bayezid's sons and the treasury from the Timurids and made their way to Constantinople. It is said that Timur himself admired the Serbs who according to him "fought like lions".
Mind you, all of this was happening while many of the Turkish troops deserted and switched sides. Serbian troops literally stayed more loyal to the sultan than turkish muslim vassals. The battle potentially could have been won if Bayezid had listened to the Serbian prince. Anyway, shortly after the battle, the Ottoman Empire would fall into civil war (Fetret Devri) and Serbs obviously used that opportunity to become independent.
Fast forward to 1453, they were once again Ottoman vassals. Now this case is much more interesting. When the Ottomans were attacking Constantinople, there were also Orthodox Serbian troops fighting alongside them. Since Serbia was a vassal state, it had to provide troops. But it also goes deeper than that. During this time the Byzantine Emperor believed that the answer to saving the Empire lied in the military might and power of the western nations. He did everything in his power to please the pope. There was a heretical union between the Catholic Church and Orthodox Churches which was opposed by most of the populace and I think Duchy of Moscow, you also have Saint Mark of Ephesus who went down in history with his opposition to it. The last emperor of the byzantines was not Orthodox, he was Catholic and betrayed the Orthodox faith. This is objective and factual. Needless to say, God punished the Greeks harshly for their betrayal. I personally genuinely believe the city wouldn't have fallen if they kept true to their faith and rejected any western influence.
I think the general sentiment around that time was that being under Ottoman rule would be preferable to being under the rule of latin catholics. The common folk in Eastern Rome felt this way. As for how this relates to the Serbs, there was a centuries long rivalry between Bulgarians and Eastern Romans. Mostly an ethnic rivalry. Serbs and Bulgarians neatly combined their political antagonism towards Eastern Rome with correct theology and that's probably how the average Serbian at the time would justify fighting on the side of Ottomans.
On the eve of the fall of Constantinople, the Grand Duke Loukas Notaras proclaimed: "
I would rather see a Turkish turban in the midst of the city (Constantinople) than the latin mitre."
This view, the idea that Turkish rule was better than any latin rule also went back further. In 1275, after efforts were made to submit the Orthodox Church to the papacy, the sister of Emperor Michael VIII is recorded to have said: "
Better to destroy the Empire of my brother, rather than the purity of the Orthodox faith."
And finally, the patriarch of the Greek Church right after the city fell, Gennadios Scholarios, shared the same view.
The fact is that the Orthodox Church with its unity and its hesychastic theology was maintained through 400 years of subjugation under Ottoman rule, and this unity is what prepared the Greeks for independence. While the Greek Orthodox population of lower Italy and especially Sicily, the so-called Great Greece, lost their Orthodox faith and Hellenism. So, despite the wounds of Ottoman rule, the view of Loukas Notaras, St. Mark of Ephesus, Michael VIII's sister and Patriarch Gennadios Scholarios was proven right. Ottoman rule prevented the latinization of Orthodox nations.
I apologize if it seems like I went off topic, it's just a really interesting thing for me.