More importantly:
> reasonably nuanced philosophical perspectives are by no means incompatible with belief in supernatural evil...
There are a lot of ways to take this, so just to be clear, are you saying that you believe an all-loving and omnipotent god created a willful being of pure evil?
My clarification to your last question is to fall back on the traditional understanding of evil, going back to at least Plotinus: evil is real, but it's a derivative reality, parasitic on good. So you can't have a being of pure evil: it's sort of ruled out (in this understanding) by definition. What you can have is a being that, through the good of free will, chooses lesser goods - in this case, itself - and in the process corrupts itself and effectively revolts against its Creator. Evil, yes, but not pure evil, and not originally created as such.
It's not as if this line of defense doesn't have its holes, but it's plausible enough that I don't think it can be dismissed out of hand. And it also explains enough that, given my other philosophical and theological predispositions, I tend to think it (or something like it) quite probable.
It's a natural interpretation for anyone familiar with the Euthyphro, but most people have not read Plato.
I haven't generally seen strong evidence that adherents have actually adopted the beliefs professed by apologists. Surveys routinely find adherents generally fall closer to literalists.
Gallup found that 70% of Americans believed in the Devil, similar numbers for hell.[0]
It might be tempting to wash this and say, "no, all those people just meant a metaphorical devil." But if you step back, it strains credulity a bit to argue that people, when asked if something existed, would respond "yes" to mean "not really, only in an allegorical sense."
Mostly though, of all the rationalizations offered for odd religious views, I just haven't yet seen any good evidence that most adherents have actually adopted these more nuanced views.
[0] http://www.gallup.com/poll/27877/Americans-More-Likely-Belie...