As you get into the higher levels, your race becomes less and less important (not that it was all that important to begin with). Although you will still have considerable stat differences between classes less suited for the job, yout abilities will overweigh them.
However, I would strongly suggest not subbing a WHM with a melee job, such as DRG (unless farming). It is a waste of a sub, since you will neither be picked as the main meleer, or the main whm.