I think that what DW is using is a kind of bow hold that's traditional in Poland and other parts of Eastern Europe, but.... and I'm just an amateur here... as amazing as his playing and talent is, he keeps that hold for 30 years and will be dogged by tendonitis and other hand/arm/shoulder issues. IMO
There is no reason any more for anyone to be playing, French or German, without a loose, open, weight-not-squeeze hold. We know what the instrument can do to us!