Creo has some very course approximation dependent on part accuracy. These are very prominent in equations like involutes. There are also areas where you may input a formula but the data entered is only the accuracy of your current number of digits. All are correctable, but you have to be aware of them. So far, I've had pretty accurate results.
Although the formula available provide a perfect interface, you must also account for the deviation tolerance. The formula should therefore represent a maximum material condition. Once you have the "perfect" shape, offset the face to the allowable backlash you can tolerate. Then mirror and pattern that feature.
Depending on how you plan to mount the gears, you can always have some adjustment for backlash. You will be amazed at how forgiving a gearset will be unless you really push the structural limits.