Aaron may not be the kind of mentor parents would want for their kids, but he's definitely an influential character. It's Aaron who suggests that Chiron and Demetrius rape Lavinia in the woods (2.1.10). He even brags about it later: "Indeed I was their tutor to instruct them. [...] That bloody mind I think they learn'd of me" (5.1.9). So Aaron is a guide alright, but he's the kind of guide who leads others astray.