Well, maybe if the scaley bit were right around the elbows and shoulders and wrists, all the places you usually twist and bend, it would be more practical than if it was all over, maybe?

I don't think Veela need armour. But they would look brilliant in it. Even shinier than usual. Or, well, if he liked snakes so very much, perhaps he was planning on creating an army of cobras and pythons and such.