Schoeman, who secured the bronze medal in the same event at the Athens Games in 2004, won his heat in 21.92 seconds, qualifying fifth fastest for the semi-finals, while Louw was 11th fastest in a time of 22:12.
Karin Prinsloo also progressed to Thursday night's semi-finals, finishing fifth in her women's 200m backstroke heat and qualifying 13th fastest in two minutes, 10.34 seconds (2:10.34).
Wendy Trott failed in her bid to qualify for the women's 800m freestyle final, finishing fourth in her heat in 8:28:98.