I took that class from the other instructor, who had us use OCaml instead of Java (as I presume Aho still uses.) The Dragon book was interesting, but, for the most part, we were able to get on from the in-class slides.

I don't think there's anything wrong with having Discrete Math, Data Structures or Computer Science Theory as pre-requisites for PLT or a compiler class. However, I doubt the necessity of OO Programming & Design and (so-called) Advanced Programming.