Scott,
I know exactly what you're talking about and have even witnessed it in concert. Yes, they use a smallish mallet on their Wuhan. But more to the point, I think they picked out one that decays very rapidly, which works extremely well for "Salome" and "Wozzeck" - two big specialties of the Staatsoper. Believe it or not, the way you suspend a gong can slightly effect the decay time as well. You can do this by 'doubling' the rope through the drilled openings, or by simply using a very thick rope. In essence, that helps to 'dampen' the gong.
This would make sense for two reasons. First, they like to play their percussion from a seated position - something that Mahler hated, by the way (he played percussion at the Vienna Conservatory). Second, there simply isn't much room in the opera pit to be hanging all over the gong in an effort to dampen it quickly.
If all this sounds far fetched, just listen to various Vienna recordings of either "Salome" or "Wozzeck". You'll hear what I mean.