Straight d20 using the standard D&D classes seems like an odd choice for this subject matter. I like the idea of RPGs taking a more literary bent, but I would have to take a real close look at this one before buying it. A simple grafting of Dante onto D&D could be kind of painful. I mean, druids, rangers, psionics, bards, clerics casting raise dead left and right...
It almost seems like an independent OGL game like Slaine or Wheel of Time would be more appropriate.
If you were familiar with the original Abyss game, it was a lot closer to "D&D in Hell." I aim to change that but still intend to retain the combat-oriented nature of the d20 system. It's not a simple grafting, certainly.
The nine circles are like mini-planes. Each PC picks a plane based on his mortal life. Those choices determine the availability of races and classes to choose from. On his "home" circle, the PC is most effective. As he travels up and down the circles, his powers diminish. To take your examples:
* Rangers and druids end up on Limbo. Here, they can cast spells and use their full abilities. But it's a wild, dangerous place. The wild nature of supposed "pagans" rules here. Animals are bigger, the weather is more dangerous, the terrain is more extreme. As druids and rangers stray further from the first circle, they can't cast as many spells. A druid on Cocytos, the ninth circle, can only cast 1st level spells.
* Psionicists get treated like other spellcasters, daming them to the Malebowges. There, magicians are forced to walk with their heads twisted on backwards. In the Malebowges, any arcane spellcaster or psionic manifester can turn his head 360 degrees. The eighth circle is also home to all manner of thieves and liars. Which is why...
* Bards end up there too. Lying, and indeed, every deception is easier in this circle, so bardic powers work best there.
* Clerics end up in Dis, because they wouldn't be there if they had worshipped the right deity. As a result, their powers work but diminsh in effectiveness as they stray from Dis. Fortunately, Dis is the sixth circle, so clerics are never in too much trouble.
And raise dead? Fuggeddaboutit. In Hell, there's disincarnation. Nobody dies, they just get "devolved" into a larva that is also used as a form of currency. Certain really extreme situations can destroy even the soulstuff that constitutes PCs. But on the other hand, if you didn't like a guy who just "died" you could probably sell his squirmy little maggoty self for a profit.
In short, the systems blend quite nicely.