Chop Chop gets his origin, and his true name revealed, in the Bob Haney, Dillin and Cuidera story from Blackhawk 203 (Dec. 64).
Pretty much any tale dealing with Chop Chop before the 90s was racist to a greater or lesser degree, though this is not as bad as it might have been. After escaping from a concentration camp, the Blackhawks get sent to China on a mission against the Japanese. Their goal is to persuade a Chinese warlord to join the fight. As soon as they arrive, they encounter the costumed White Dragon, who is leading attacks on the Japanese.
The warlord is not inclined to join the fray, explaining that as long as he stays neutral, the Japanese will not attack his people. His son, Liu Huang, feels the same way, but is more openly rude to the Blackhawks. This, however, is clearly Chop Chop, so it's easy for the reader to get ahead of the characters, and deduce that he is also the White Dragon, and lying to conceal that fact, while fighting against the Japanese.
And that all gets revealed as the story goes on. Once his identity is known, Liu Huang wants to join the Blachawks, and has to fight each of them in order to prove his worth. His martial arts skills come in handy here, but are also the basis for the team giving him the nickname Chop Chop.
By the end, the father has come to see that he and his people must join the fight against Japan, and he also agrees for his son to go off and join the Blackhawks. Ever since the costume change, Chop Chop has been dressed like the other members of the team, and this story backs up the notion that he is a full member, not just some mascot.