No problem:
Access to the First Class Terminal at Frankfurt Airport is only possible if you have a
confirmed First Class flight on Lufthansa or SWISS or, for
HON Circle Members, on Lufthansa, SWISS or Austrian Airlines flights
with a same-day departure. Passengers arriving at Frankfurt are not permitted access to the First Class Terminal.
http://www.lufthansa.com/de/en/Loung...mation#ancAbT1