The achievement "Sullust Interception Mastery" is bugged, I think. It has a bonus requirement (0/1 Decimate Republic Forces) that doesn't exist, and thus can't be completed. Also, on the Republic equivalent (Drexel Sweep), this bonus objective doesn't exist, which might prove that the imperial conterpart is indeed bugged.
Also, the text on the achievement "Drexel Sweep Mastery" is wrong. It says "Completed all bonus objectives associated with the "Fondor Escort" Republic space mission", while it should read "Drexel Sweep" instead of "Fondor Escort".