Hydrolyzes N(G),N(G)-dimethyl-L-arginine (ADMA) and N(G)-monomethyl-L-arginine (MMA) which act as inhibitors of NOS. Has therefore a role in the regulation of nitric oxide generation (By similarity). H2O + N(omega),N(omega)-dimethyl-L-arginine = dimethylamine + L-citrulline Translocates from cytosol to mitochondrion upon IL-1beta stimulation in chondrocytes. Belongs to the DDAH family.