Hi Ted,
Thank you for bringing this to our attention.
From the block diagram on page 10 of the datasheet, it looks like the high side gate driver is driven by either VCC or VCCX, but it is not clear what drives the low side gate driver. I am looking into this, but it may be the internal VCC, which is 5V. If that is the case, the Vgsmax rating on the boost FET may not be an error.
If you disconnect VCCX, the high side gate will be driven by the internal VCC of 5V, which may not be enough.