Weirdest kid show appearances
The common theme of the list is that actors who usually appear in adult shows or using adult humor are appearing on children's television where it is unlikely they will be recognized by the average viewer. Frankly, I doubt most kids recognize most celebrities when presented in front of them no matter what they've appeared in unless it's on The Disney Channel or Nickelodeon.
I think the point of appearing on these shows is greater visibility for the actor. That way, the kids might recognize them when they're older and discover comic gold like Strangers With Candy or Curb Your Enthusiasm.
Most of the instances in the list have the actors playing characters anyway. My guess is that their appearance on these shows is more for the benefit of any parent who might be watching alongside their kids. The parents can see these "notorious" celebrities on a kid's show and laugh at the irony.