In my experience they haven't been quite the same. I wear a 15/34 in slim-fit dress shirts. Perfect fit for me, slim but not too slim.
I ordered a slim-fit sport shirt in medium and it felt enormous. I exchanged for an ESF sport shirt in the same pattern and it fits like a dream. Very close to the slim-fit dress shirts for me. I would sat that the sport shirts fit a little larger/looser than the dress shirts in general.