There is a point in the game where you either talk to Panther or Hawk about Maniac. Both of them are sick of him and you have to decide if you'll talk to Maniac or let them deal with him. I chose to talk to him the first time and saw the video of that with Catscratch but I never saw anything if I chose to let Hawk and Panther deal with it. Did anyone else see something happen if you chose to let them handle it?

Depending on which branching path of the game you take, either with defensive missions in Circe following Panther's advise, or aggressive commandeer/looting missions in Speradon following Hawk's advise, you'll talk with the colonel who you sided with.

As with many on-board inter-mission cutscenes of this type, the conversation has nothing to do plot threads, but rather with in-mission morale of your wingmen. I.E. If you tell Panther you'll speak to Maniac so he'll quit harassing her, Panther's morale will go up. If you tell Panther to deal with it on her own, her morale goes down. Morale has a slight bearing on how well a wingman performs during missions, and how reliably they follow orders.

Neither one of these conversations (with Hawk/Panther) has an effect on the Maniac, or the plotline with Catscratch.

It does have an effect on the ending you get though.

Yes, depending on whose morale is higher (Panther or Hawk), you get one of two different endings on the "winning" path. The more you agree with them or act supportive in conversations, the greater their morale. Often you have to choose one over the other.