In the second picture of Serbian Chetniks posted here by SerbianArmy,
more precisely in the one up above General Ratko Mladitch,
you can see the Chetniks of Manda, a Serbian Chetnik leader.
The one fighter at the extrem right of the picture
wears a Magen David on his breast.
Is he, perhaps, one of the Jewish Volunteers fighting alongside the Serbs ?
Concerning the Serbs letting their beard (and hair) grow "wild",
it is a sign of mourning for the endangered Country,
since, in funeral habit, when a relative/parent dies,
Serbian males let their beard grow this way.
I think only Serbian Officers, among the Chetniks, are allowed to let their beard grow this way.
That's why photos (of chetniks) can be seen
with the majority of men not wearing beards, just a handful of them.