These reports don't make much sense to me.
The incident occurred 400 nm from the border of Romania and 580 nm from the border of Poland. Standard NATO AWACS aircraft (E-3 Sentry) has radar range of 400 nm at high altitude. It might have seen the moment of impact if it were, by extreme stroke of luck, located at the closest point along the Romania/Ukraine border at that moment. If they were any further, they would not see even that, because even MH17 itself would have been below the horizon for E-3's. As the Spiegel article points out, MH17 went out of range of AWACS 30 minutes before the crash.
Given all this, I'm puzzled by the statement about a missile "that was tagged as SA-3". Where was it observed, and by whom? If it was observed by AWACS, it wouldt follow that it's a totally unrelated missile that was launched somewhere far from the incident, e.g. by the Polish military (they do have some SA-3's left). If it was observed near Donetsk, then the German military is omitting some crucial facts.