Regaridng basic pwm operation, the transistor voltages are only determined by the converter input voltage, there's no difference between e.g. 5V and 10 V output regarding switcher voltage levels, just a different voltage level.
It's not explicitely specified in the datasheet, but implicitely Voutx pins are limited to Vcc (as "other" pins in maximum ratings). This means they can't be used for output voltages above 5V and must be grounded, which sets device operation to forced PWM. If you don't need the power saving features, this might be a way to operate the device with higher output voltage.