While that may be true, China is not going to agree to a unified Korea IMO unless the ROK agrees to boot out all US military personnel. The last thing China wants is US troops on its border. Probably one of the biggest reasons China tolerates NK is that is serves as a buffer to US forces in the ROK
I think that would be part of the deal. South Korea gets help from China in easing the transition, in exchange for kicking the US troops out. Reunification is going to cost a ton, as the Germans found out. China is willing to make that investment.