If you crash on the Nurburgring an ADAC truck from the local agent - Bomgard - will recover you. Note that this is very much cheaper than trying to limp round with a broken car: see Fluid Leaks.
The standard recovery fee (excluding ADAC members) only gets you back to the car-park - if you want to be recovered on anywhere else, you are strongly advised to agree the additional cost in advance, as the rates can be high. It is usually best to arrange your own onward-recovery once off the track.
ADAC is the German equivalent of the RAC or AA in the UK. It has a reciprocal arrangement with the AA so you can join as a UK member and it will cover you here and in Europe. If you are an ADAC member you should be able to present your card and not pay the €250 standard recovery cost if you crash on the Ring. It does not appear to be possible to sign up online but the telephone number is +49 941 52344 and the staff there speak English
More details are available on the ADAC website.
In 2008 ADAC suspended its involvement with the FIA over the scandal surrounding Max Mosley and his subsequent retention as FIA president. ADAC is the current title sponsor of the Nurburgring 24hr race.