I'm pretty sure they won't care at all about that, either.
The AUSA cares about trial experience. They also care about pedigree - what work you've done (hellooo BigLaw), etc. There is often a split among AUSAs in that some care more for your pedigree while others find experience in the trenches more important (i.e. the number of hours you've actually spent in a court room, and whether that was handling felony cases as a prosecutor, etc.).
A third factor, obviously, is that who you know and your reputation can make an impact to some extent.
As for the board certification thing, I think it's unnecessary, but I've never specifically asked for it. I skimmed through the "requirements" but the fact that you pay $800 for this is ridiculous. I'd probably save my money, if I were you. The requirements, like being lead counsel on at least 5 jury trials, etc., are things you should just be doing anyway to become an AUSA. Paying $800 (to the friggen ABA of all people) for some redundant fluff on your resume seems pretty expensive and wasteful, IMO.