It depends what you mean by redlining.
Avoiding neighborhoods for racial reasons has been outlawed, whatever one might think of that. But I should think that a real estate agent has some obligation to warn his clients about serious dangers, such maybe their kids are likely to get killed if they move there.
You are right. Any responsible person would look out and advise clients of potential danger......Just carry around police reports for particular neighborhoods and discuss as a matter of conversation with the client.....The feds can go jump.