Further update for those who may find this thread on a search:

I called a few of the hotels on this list: http://www.frankfurt-airport.com/con..._airport2.html

...and the Steigenberger hotel said for 24EUR, one can access pool, fitness and locker room facilities. They claim to have a shuttle every 15 minutes and that' it's a 5 minute ride to the hotel.

Assuming the locker room facilities are inadequate, are there any options for storing hand luggage at FRA? Either in the FCL, SEN lounge, or for a fee?