OD&D is rightfully known as being sparse when it comes to both details and its rules. When those two categories of sparseness come together, it sometimes leads to head scratching. A good case in point is this cryptic statement from Volume 1 of the three little brown books: "Note that clerics of 7th level and greater are either 'Law' or 'Chaos,' and there is a sharp distinction between them." (And before anyone points this out, yes, I know this version of the lines comes from a later printing, one that post-dates the supplements, but bear with me here). This implies to me that, in OD&D, Neutral is not a valid alignment for a cleric, at least not one who wishes to get far in his hierarchy and command great powers. AD&D specifically excludes True Neutral as an alignment option for clerics. Greyhawk introduced druids as a monster type and notes that they're "priests of a neutral-type" religion. Eldritch Wizardry opens them up as a player character option, but limits them to the neutral alignment.
Taken together, it's all very suggestive, as if there were some kind of specific understanding of alignment at work here. I know that's probably not true at all, but it doesn't change the suggestiveness of it all -- a suggestiveness that Frank Mentzer spun in a very interesting way in his edition of the D&D rules. His Companion Rules druid is a kind of "proto-prestige class" that's parasitic upon the cleric class. Druids are Neutral clerics who abandon their old faith and embrace the ways of Nature. in the process shedding some old abilities (like turning undead) and acquiring new ones (such as new spells). I think Mentzer's druid is a riff off the old OD&D rules about clerical alignment and I've always rather liked it. In Dwimmermount, druids -- and Nature -- stand outside the battles of Law and Chaos. Consequently, they're generally regarded with suspicion by most folk, particularly those siding with Law, since they have a "with us or against us" mentality.
I haven't yet introduced any druids into my campaign and may never do so. Still, I have been thinking about them and what their class will be like. It'll certainly be based heavily on the Supplement III version of the class, but there's a big part of my that really likes the notion of druids as made up entirely of formerly Lawful or Chaotic clerics who've abandoned their old faiths and adopted a new one. There's something very Moorocockian -- something very rebellious -- about this approach that appeals to me. The trick, though, is to ensure that the druids never come across as hippy-dippy, kumbaya types. I frankly hate that conception of the druids and it's certainly not one that belongs in a setting that takes its cues from swords-and-sorcery. Instead, the druids will indeed have a certain nobility to them, one that's mixed in with a certain cruelty and inhumanity. These are people, after all, who turned their backs not only on the gods but on humanity as well, throwing their lot in with insensate Nature, which cares not for the fate of neither men nor mankind. It's a harsh, unmerciful philosophy and Law has good reason to view it as every much as big a threat as Chaos.