Can I use the official wallet to recover bitcoins sent to an alternative wallet? I like alternative wallets like Armory and Electrum because they offer more features, some of which are fundamental for security and convenience. But I'm a bit worried about them not being "compatible", I mean you can't import an Armory wallet into Bitcoin-qt.

So what I would like to know is whether it is possible to recover my bitcoins (which if I didn't get it wrong, they are in the blockchain and could be spent with the private key) using the official wallet. For instance, the paper backup generated by Armory contains a "root key" and a "chain code". Is one of those the private key or what?
Most alternative wallets give you the possibility of exporting the private keys. Private keys can be imported in almost every other wallet.

In the case of Armory, the root key and chain code are used to generate a whole chain of private keys. You can ask for new addresses as you like inside your wallet, and by backing up only these two keys, you can recover all of them. This is a useful feature, but makes it harder to import in other wallets.

Luckily, Armory has an option to export the individual private keys of all the addresses you used. In the wallet menu there is a link "Backup Individual Keys" for this purpose. This exporting feature will always be available, also when Armory decides to stop, since it is independent of Bitcoin itself.

I don't know how other wallets support backing up individual keys, but I suppose most of them can.