I am a tax man also in China, now is waiting for second letter. I don't think have been working for government will be a problem, don't believe that. lots of people had experience working with government, some are police men, they are now living in CA.
I guess one reason could be your part-time working experience in the US, which may imply that your profession (tax advisor?) may not have a better chance to find a job in the US, so you need to convince the CIC officer that you won't have problem to be employed
Drop me a line if you'd like to exchange. allannyc@yahoo.com