Most essential oils are toxic to cats. That is the safest approach to take. The problem with using them on things like pillows is that the cat can still get it on their fur, and then lick it off. This is probably a good question for the vet - the internet has some really good information, and some really bad information. Some sites on essential oils are honest and say NOT to use them on cats, and still others insist they are just fine, which they are not.
many years of cat rescue