The Skywriter ( full sized ) has an onboard 3.3v low dropout regulator, so it'll work with either a 5V or a 3.3V power supply. All of the data lines are level shifted, so they'll also be fine.
So, yes, it's in specs because it's always going through a 3.3V regulator. When you power it at 3.3V it's actually running the chip even lower! ( which is still in spec )