That is correct, ERC 20 Tokens are just linked to an ethereum address so any ERC 20 Token can be held on ledger wallet. Currently they don't have steem support, but they are leading the pack in hardware wallets and have the best support (IMO) for current and future coins which means that it is only a matter of time before they add Steem support. I forgot to mention but the ledger nano s can alsu be used as a 2 factor identification device much like google authenticator, which would let you lock up your steem if it is in a wallet that is compatible with 2FA.