This is a fluff question as well as a tactical question to add to my current growing harlequin army well I was reading both books and it looks like from a fluff perspective they are very similar in the way they work with some difference I guess to make them not the same army but they both hunt and hate chaos they both are very hidden away but harlequins are more open about there existence then grey knights.
So for instance would they team up or use each other for there personal gain?