I’m not familiar with the song, but there is no rule that says that choirs or classical musicians don’t work with traditional songs.
Skalkotas for example is known mainly for his Greek Dances and Greek folk dances works.
Other than that, choral groups are not very common in Greece, but there are some professional and semi-professional choirs, more often in Western Greece. Of course they are not traditional because in ye olden days people did not gather in groups of 20-30 to rehearse and sing popular songs in slow motion (church music is a different story).
There is also a tradition of polyphonic singing in the western Balkans, and that includes Epirus, but it is limited and was not very well known in Greece when I was young. I think people started paying attention to it at the same time as they discovered the Balkan tradition of brass bands from places like Florina. People will also tell you that Corfu and the rest of the Seven Islands is different because of the Venetians etc. But Patras, where I come from, has several choirs. So it is probably a western Greece thing.
A friend of mine used to sing with the Μικτή Χορωδία Πατραϊκής Μαντολινάτας and of course our school had a choir and if you were in the choir you had a guaranteed 20 in Music, which may not be an examinable subject for university entrance, but it boosts your grade average. Those of us less fortunate with our voices had to actually pay attention to music class if we wanted to boost our grades. I recently found out that out music teacher, Miss S, who was already quite old when I was in school, died. She was tall, thin and had a very croaky voice, something between a frog and a crow, but of course she had perfect pitch. She and some other old-maid-music-teachers used to buy front row seats at every music event in Patras and they would all parade in at the same time, looking super dignified and contemptuous of the plebs who clearly did not know anything about music and were there just because there was no other worthy entertainment in town, whereas they were there because they could Understand Music.