Keep in mind, also, that, when it comes to programming music formats, knowing how to interpret data and working with people are more important than knowing the music itself. With good data, even a mediocre programmer can look great. If anything, not being an expert in rock might help Devin because he won't be under any illusion that he has a golden ear, which has been the kiss of death for many a PD.
Plus, as others have mentioned, he probably will just be working with the PD of WEGR. If he looks at the same data as the PD, that's not likely to hurt anything. Another set of eyes on the same data helps far more often than it hurts.