Hi Henry,
There is definitely a First Class section in the DB lounge at Frankfurt Main station with free snacks, drinks and wifi. You get a 2 hours wifi pass similar to the ones in the LH lounges. The wifi is not only free in the First Class section. If you have a voucher you can use it in the entire lounge.
There is no separate first section in the DB lounge at Frankfurt airport though and the lounge is nothing special anyway (no nice view).
Enjoy your trip.
Cheers,
totti