OP does not mention on what ship they will cruise. On the classic ships, Magic and Wonder, the Concierge staterooms are mixed in with regular staterooms. You need to pay close attention to distinguish them (they have a doorbell, or a sign for the Walt and the Roy suites). We've often seen FE's on Concierge staterooms on those two ships.
On the newer ships, Dream and Fantasy, the Concierge staterooms are in their own section. While not blocked off to regular guests, they are not hallways used to go somewhere else on the ship. We've rarely seen FE's in that section of the ship, but they can be accessed if you wish to hang one up.