I took off to investigate some of this, since it seemed to me very surprising that Jow Ga would've had Bak Mei in it in any kind of way. I should've been able to see it if there were, I thought. So this is what I found:
Dean Chin started learning martial arts at the age of seven, he started with Jow Ga when he was nine. In the thread you linked someone mentioned Chin having taught Sap Ji Kyun, the "Cross-Pattern Form" to his advanced students. Now, Sap Ji is often the first form taught to new students in Bak Mei and does not yet train any of the distinct Bak Mei power generation. Furthermore, it is not an "original" form in the style and was borrowed either from Lam Ga or Lei Ga, both of which Jeung Lai Chyun studied in his youth. I do not know whether he continued with Bak Mei after joining Jow Ga, but so far I've only heard an account of him teaching elementary material. Seeing his forms list might help with it.
Jow Ga in Vietnam then seems to be limited to Hanoi in Northern Vietnam. Bak Mei has only been introduced to Saigon in the Southern part of the country by one of Jeung Lai Chyun's early students. I have never heard of Bak Mei in Hanoi (but Wing Chun/Weng Chun, yes).
There is actually an example of mixing Bak Mei to other arts. Fatsan Bak Mei seems to be a hybrid of Choy Lee Fut hand techniques with Bak Mei stances and principles. The result is distinctly BM, but you also see lots of waving hands that are not typical. Below one of their original forms:
I'm not trying to debunk anything here, I'm just trying to figure out of what I know already and how does new information fit into it. If you can help me out with more tidbits of knowledge, I'd be happy.
This is starting to stray from the topic of the thread, but how is Shaolinquan visible in Jow Ga? I have a friend who's been going to China for about ten years to train the old-style Shaolin boxing, and I'm hard-pressed to see commonalities with the two. However, Jow Ga has to forms that are identical to Shaolinquan in name: Siu Hung Kyun and Daai Hung Kyun exist in Shaolin, (the former is even their most important core form) but the Jow Ga versions are actually different forms than ones in Shaolin.