I dont think the topic will come up. If the writers were going to bring that aspect up it would have happened already. I just dont see how it could be brought up in conversation.
Would Dexter volunteer that info? No.
Would Deb ask that specific question? No.
Do you wanna know why he won't tell Deb that he killed his own brother? Because he is becoming human and is trying to reunite the peace with is sister, and doesn't want to let her down or make her feel bad. "Rudy" was her boyfriend for a while...