That pledge is as good as toilet paper. Don't be so naive. (And that's not because they're chinese. All governments would immediately disregard such pledges at the time it was deemed necessary to strike first)
Fact remains they have never deployed them. I am no fan of China, but Hey at least they say they won’t deploy as opposed to certain other countries (for eg. India’s immediate neighbor)
If America tried to invade China using conventional weapons, then I believe China wouldn't rule out responding with nukes. But yeah, I doubt they would use nukes in a small stakes dispute.