Maik have you already tested that Undead or WE are hard counters to Crone decks? I'm especially curious how adding hp to the capital with Wildwood Grove helps you against milling.
No proper tests yet, and I would not go as far as calling it a hard counter without that. However, I'm quite sure that mill decks are weakened against Undead, with the following reasoning:
Milling hurts you because a) your opponent wins when your deck is emptied and b) you are losing cards that might have been crucial to your plans. For the Undead, b) is clearly less of a concern, since there are a lot of cards you'd rather see on your discard than in your deck or even in your hand. And Necromancy moves cards from discard to deck and thus obviously weakens the impact of a). So in my eyes, it is rather obvious that milling decks will have a harder time in a meta with Undead than in one without it.
For the Wood Elves, the effect is certainly less strong and might not be important at all if they turn out to be still too weak to make tournament grade. But it goes like this: with Wildwood Grove and cards like Abandoned Mine, Long Winter and Pageant of Strikes, you can recycle cards from the discard to your hand, so the effect of b) is diminished. You can also put Ambush cards directly where you need them: as developments on the table. There is no direct mitigation of a), admittedly, except that you might need less card draws when you can play devs from discard. Going out on a rather speculative branch, a deck that treats its developments as a second hand (with the cards mentioned above) can afford to be bigger than 50 cards, which would also be bad news for mill decks.
To summarize: Undead are clearly more impervious to mill decks, Wood Elves might be. The first statement can be made wihout tests, and the second is not much of a statement, really