Oh I felt comfortable with Dexter thinking of the Ice Truck Killer as Rudy: that is how Dexter met him and got to know him (talking to each other, eating meals together as Dexter and Rudy). Brian was the true name of the brother he remembered vaguely as 'Briney'.... And of course Dexter was thinking about Deb not using any name, but if she was to use any name then it would have been 'Rudy' (did she ever even hear the name Brian at all?), the killer who kidnapped her. I guess there is always confusion when a character has different names known to different people....