Runup policies are surely operator-dependent. On the 146/RJ, when Aer Lingus served London City, they always did, the flight deck announced it. Cityjet often do. Swiss not so. I always thought it was not so much for better acceleration performance as to ensure that all the engines have stabilised symmetrically.
Neither Cityjet nor Lufthansa have had the long body RJ100, by the way, but the standard sized RJ85.