It's a bad idea to expose private keys from your chain.
Indeed, a very bad idea. Armory is designed so the use of a watch-only wallet is safe. It is **not** designed so that exposure of private keys is safe. If a hacker has access to your Armory cold storage wallet, he can watch your coins. If a hacker gains access to two of your private keys that you exported to another wallet, he *might* get access to all your funds.
DO NOT TRANSFER MONEY TO ANY WALLET UNLESS YOU HAVE VERIFIED THAT YOU CAN GET THEM SAFELY OUT.
Exporting private keys from a deterministic wallet is probably not safe.