If I had to live by what my experience had taught me, he would not know that much within the work of CCP or to some extend, China.
China is a country with core power (Not even central power) problem with this is that secret are closely guarded, and most likely it will not spill over to 2nd tier personnel.
Chances are great if this is his brother who applied asylum to the US, as he is the one actually working as Hu's aide, but even then I doubt what can he actually provide beside Wen's favourite dishes or what is Wen's wife's favourite show. Working as an aide does not mean he is privy to any National Secret, if I am the power broker, I would not trust my personal aide, as they are almost the first one to black mail you when thing went to shit.
So, if this is happened to the aide, what could the aide's brother knows about? In my view, he might be simply applying for asylum so not to be deported back to China to definitely be executed. Just like many other corrupted Chinese official