I was the Scholar who Solo'd DG.
It is indeed possible, how ever, I will admit I didn't get this idea by myself. It was actually Auuriums idea after she showed me a Scholar doing it on the RO officials on youtube. So I decided to give it a try while she was on her HP and it was a huge success. The only problem with DG is that you must teleport the angels. Which shouldn't be a problem anyway, since you can just use level 1 bolts and level 5 double casting while webbing the angels and casting. Eventually when you get good at it, you wont need HP support. HP support will become a bonus and not a necessity.
For leveling spots, I recommend places such as Ice Dungeon with double bolt, or auto-spell (which ever one you prefer). Mobbing in Prison or Courtyard with Fireball / Fire Wall, Galions (when the Roween exp is back), and many other places...
Also, no matter your tier. You should always have 2 imp and 2 siroma cards. These cards are incredibly important for not only casting, but auto spell as well. Since it will out damage Brys/Celebs by far. Especially if they are carded on Orleans Gloves (not necessary but you can).