If the repeater is using different tones for RX/TX (123/411), and you enter the input tone (123) in your radio for both TX and RX, your radio will not receive any audio from any station on that channel that isnt transmitting that tone (123) - you'll see the signal bars light up on your screen but no audio from the repeater.
***Just re-read your question and missed the whole (CH19/RPT19 part), and in short, yes you are correct - if you put tone 411 as receive on RPT19 and simplex channel 19, you will only hear traffic from stations sending the 411 code (ie, the repeater)