There is a chance you may be able to get a kelpie with no herding background (Though I'm imagine you'd only be able to get one from a Backyard breeder), but either way, this dog will have tons of energy.

I'm sure it would be good with your pets if it's raised with them; herding is a modified prey drive and herding breeds should be socialized with small animals. However, I find that herding breeds listen well and that socialization is a short process with most of them. If your kelpie has no herding instinct, it will probably be the same affect, without herding the animals around all the time.

Any breed of dog can kill a cat; I'm fairly certain that kelpies are good with other animals if socialised properly, but you have to watch their behaviour towards eachother and make sure that everything is alright. If you get the dog as a puppy, it will be easier to have it understand that the cat was there first and is dominant over him/her.