As long as the charger uses the rapid charging technology that is a part of the USB-C spec, yes. USB-C allows both the charger and the chargee to negotiate to find the best/fastest charging rate supported by both ends. That doesn't necessarily mean that the Nexus 5X will charge as quickly as the Pixel, but it will still be able to rapidly charge - again, as quickly as is supported by both the charger and the chargee.
Anything proprietary (like Qualcomm's Quick Charge) will not work.