I've followed closely another debate on cats and rats here on the forum. I'm in the same situation as you are, I have three cats and about a month ago I got two rats.
As I've had other rodents, I sort of know how my cats react to them. My older cat, doesn't seem very interested, neither he is with birds that pass near our window or with any other animals such as lizards or bugs. My other cat tried sniffing the cage of my gerbil a few years back and was nearly bitten, and I'm pretty sure she is now scared of any rodents after the incident. My youngest cat, however, would take ANY oportunity of getting into my room to take a peek at my hamster's cage, and not only that, she jumped on their age, brought it down, and due to the fall, the cage broke and the hamsters were defenseless. I know that this cat of mine will never meet my rats, because I know what she is capable of.
Anyway, you know your cats better than any of us. If you think it's safe to introduce them, go ahead, but I definitely wouldn't take the risk, since both rats and cats follow their instincts very closely. Your cats could turn from chill to curious to aggressive in seconds, and your rats could grow stressed just from their predator's smell..
But as I said, I've only owned rats for a little while. I'm sure someone more knowledge on the subject will give a better opinion! Good luck. xx