There wasn't anything provided by Delta - I ended up in the public facility in terminal 1 (the only one reachable outside security for arriving passengers). It was adequate but far from pleasant (see description a few posts back). The location's pretty well described on the FRA web site, among some luxury shops in the "mall" area. I don't remember the exact details or I'd direct you. It's a single room in the back of the men's room; there's a hostess you pay. It's cheap and you can get clean but not only is it dreary, there can be a considerable wait since it's one at a time.
I did go back more recently and based on this level of "business elite-dom" you can bet I skipped Delta and flew Star business instead (in this case Lufthansa). Their arrival facility was terrrific - only wished I had more time to enjoy breakfast.
By the way, as Sabai mentioned below, they presumably don't let in Star Golds, but they DO allow business class partners from any of their US partners - I checked specifically with the agent at the front desk for future reference and she named all 3 as OK.
Then there are day rooms at some of the neighboring hotels - not sure which but I think it was described before in this thread.
Add it up and if you need to be doing something on the day of arrival after a business flight, you need to be flying Star, not Delta. Sorry Delta, but as someone who gets the same miles for either, you've driven this business customer away.
FTF