Blue
Ravenous Bugblatter Beast of Traal
Honestly, you are playing in Hell, and if you don't play the corruption of hell on good souls, you are missing out on a lot of possibilities. The overall adventure is full of it, between infernal weapons, soul coins, all the devils wanting to offer you contract. Playing good in Hell should be a challenge, you should have to make tough choices, and it does not mean that you cannot be redeemed, as it is in a sense the crux of the whole adventure.
Absolutely.
Which does not invalidate that effectively shutting down a large and unique part of the adventure if you don't give in is bad adventure design.
Making it such that if you give in things are easier for you, tempt you along that path - absolutely. But without the ability to regenerate HPs and other bennies it basically takes a chunk of adventure material and says "you won't get to play with this". And that's not okay.
Temptation as a "this is easier / better" is one thing. Temptation that is a barrier to a unique recurring experience in the module is another. Temptation for the character should not get in the way of enjoyment for the player.