Greeks and Serbs has fought wars together since ever, starting with first and second Balkan war, the world war one when Serbs actually liberated Thessaloniki after Greeks and French saved thousands of Serbian soldiers giving them food and place to stay until they recover from a March from Serbia over Albanian mountains, WWII none of us were in a position to fight really and it is continued these days, of course religion plays a role just as it does with Russian, but again, more of a tradition, there were always Russian soldiers/volunteers in all the wars Serbia fought just as there were Serbian soldiers/volunteers in any war that Russian fought including the very last one in Georgia.
This is the quote from the Time's article:
A tall, athletic Serb in his mid-40s, with blue eyes and curly long blond hair, comes into the courtyard. He walks over to the group of Cossacks, picks the oldest one out of the group and gives him a big hug and a kiss on each cheek. According to two of the men in the courtyard, the Serb, who is wearing new fatigues and slightly worn Asolo hiking boots, had fought Bosnia and is now there to fight in South Ossetia and Georgia. He may have fought in Chechnya, but no one will say. I talk to him for a moment. He speaks some English but is more comfortable in his lightly accented Russian. "I've come to fight in South Ossetia alongside the Russians," he says.
It's a tradition, and so called Russian-Serbian brotherhood, nothing else.
And another fairytale about massacre Greeks and Serbs commited:
It is what Hellenes have long feared: the shattering of a conspiracy of silence that has surrounded the role of Greek volunteers who proudly flew their flag at Srebrenica, after participating in Europe's worst massacre since the Second World War, when 7,000 men, women and children died.