In Greek a 'gamma' is a hard 'g', but it's a little more complicated.
The pronunciation of two gammas back-to-back is 'ng' as in 'sing'. So you'd need to know how it's spelt in the Greek alphabet. If he writes his name 'Vaggelis' then Vangelis is just an Anglicisation.
Find the name in Greek script. 'G' is always hard.
P.S. In modern Greek a 'beta' or 'b' is pronounced more like a 'v' so for all I know he may write it as 'Baggelis'. That won't change the pronunciation though.
In Greek: ?a??????. So with a double gamma, and so as William said, it is pronounced with a nasal 'g'. As in Singapore, but deeper in the throat.
Yes, it's a little gutteral, not truly a hard 'g' but not a softie like in page.
The trouble is that there was ancient Greek, then modern, and then a 'scholarly' approximation of the lost ancient for reading purposes only. It's the modern one we need here.
As an American of Greek ancestry, yes -- the v is softer, halfway between v and b; the a is pronounced as "ah"; the ng is very light on the n, using the back of the tongue rather than the tip, with a softer g (imagine starting to form a hard g, but the tongue never fully presses against the roof of the mouth); and "elis" is pronounced "eh-leess." In the full form of his first name (Evangelos) the stress would fall on the "VAN" syllable.