Actually, the Dresden Files example may be mine-able for more than just the Warlock concepts.
Michael Carpenter, a secondary DF character, is clearly a Paladin, as are the other Knights of the Cross. Harry (and possibly others) is quite aware of the magical effect Carpenter can have simply by speaking a prayer. AFAIK, he doesn't really "know magic," but the strength of his morality, referenced and demonstrated many times, is great enough to let him see and do things no mere mortal can. One of the others (Sanya, who wields the Sword of Hope) is an atheist--but the strength of his conviction, his earnest desire to overcome the evil he committed earlier in his life, makes his actions powerful. It may be that divine agency is involved to some degree--after all, the sword has a nail of the True Cross in it, and was given to Sanya by an archangel, and Sanya happens to be descended from "royalty" (Saladin, specifically).
Contrast both of these with Harry: someone both trained in magic, and enabled to access certain kinds of forces for various reasons, e.g. Hellfire and Soulfire and his Winter Court dealings. His powers have little to nothing to do with a purity of purpose or devotion to a cause. Instead, they relate to duties he is magically bound to perform, lingering influences of powerful entities he's interacted with, or knowledge of/access to a power which enhances the magic he can already do, specifically so he can perform a requested task.
We might then say that there is a sort of spell spectrum or space, rather than a really strict line between the two--though again I am cautious about fuzzing the boundaries. Wizards represent pure "magic-by-knowledge." Paladins represent pure "magic-by-devotion." Clerics are high on the devotion, but still have a significant "study" component. Warlocks don't have "devotion" per se, but there is a sense of attachment to otherworldly beings; they do, however, specifically seek out lost tomes and forbidden knowledge (the whole Dr. Faustus thing), so they're high on the "knowledge" scale but for reasons different than Wizards. Sorcerers "know" in a purely intuitive sense, though there are small traces of 'devotion' for at least some kinds (Storm and Cosmic, for instance).
From there, I would then say that the majority of gods, or at least a majority of those that are neither Chaotic nor Evil (so LG, NG, LN, and TN), select/prefer people who are high on the "devotion" scale and thus are not especially interested in "creating" Warlock, Sorcerer, or Wizard helpers. Bahamut is an especially bad example, IMO, because he's LG and therefore likely (IMO) to oppose granting power to someone just because it would be "effective" or "practical" or the like. He seems like a very Optimus Prime-y kind of guy--you do things the "right" way.
A different god--let's say Kord, for instance--might be totally okay with letting slip One Weird Celestial Trick etc. He'd probably think Wizards are a little too stogy for his tastes, but I could (maybe) even buy a Sorcerous bloodline coming from the STRENGTH OF THE STRENGTH GOD, RAWR.
Druid (and Shaman and a few other things) poses a somewhat thornier problem because it's more edition-dependent. Bards are also kinda hard to place on this scale, though I'd put them pretty much solely in the "magic-by-knowledge" axis. They might be 'devoted to song,' but it's not really a "purity" thing per se, rather a commitment to enhancing one's talents.