I believe the original meaning is that dogs and cats can be good friends for a person (собака- друг человека), not among themselves. The wording is kind of awkward, though.
Well maybe... Still not easy to translate though - again due to 'opposition' of cat and dog in Russian. Собака - друг человека - yes, but кошка - друг человека is nonsense idiomatically. So maybe: Они могут быть хорошими друзьями человека or Вы можете найти в них хороших друзей - but again, being grammatically correct, these sentences do not sound Russian at all...

SY, Григорий