The Ring has inconsistant times overall because some runs are done in the rain, and poor conditions and some with inexperienced drivers, and others done with specially prepared cars.
The one SRT-10 Viper test was done with a German driver who was experienced with the track, but totally new to the SRT-10 Viper, and subsequently he got relatively crappy numbers.
The Ring is only a good judge of performance for cars that are regularly campaigned there. Porsches are run on the track most every day, so the sheer numbers balance out the day, experience, weather, prep, variables.
GM realized the European (and world) value of being seen with good Ring track times and so they campaigned the C6, Z06, and Cadillac CTS-V there with engineering crews and professional race drivers, and got relatively good track numbers,
I do think that Dodge should campaign the new Viper there, but I think that they have held off so far because of the obvious comparison to the high performance Mercedes cars. If the $90K Viper beats the $450K SLR on a famous German racetrack it could be embarrasing for them.