4-pin fans can plug into 3-pin headers without any problem. They will even ramp if the header supports it, it will just be voltage ramping rather than PWM. In the end, the fan might be slightly less efficient and louder, but not by a noticeable amount.
So, you will be just fine using that fan on a 3-pin header. Just make sure you get the right 3-pins plugged in to the header. The blue wire will be the one that isn't plugged in to anything.