When analyzing the song "Hangar 18" by megadeth, I noticed an?
It is a fairly common way to transform the dominant into a more powerful one (it should get your attention when you hear it). The next chord would most likely be some form of Ebm or Eb (the tonic/temporary tonic in case of another key signature). Its not dorian, but rather just harmonic minor (minor scale with maj7) and the Bdim/D is actually a Bb79/D without a Bb, so it functions like a dominant in Ebm or Eb. It is a chromatic movement, yes, for the bass.