I really wouldnt do arpeggio's on the bass. And on the off-chance that your talking aboutweep picking, it's out of the question. also, In general, it doen't work to well. The bass's main job is to hold down the rythm and play the root note in the chord progression that makes up the song. Thats your plain, basic, bass player. you can improvise doing scales in the key of the song but make sure it fits and dont get in the way of the rest of the band. If you guitarist is doing a solo, it is best to do something simple as to not complicate/ mess up his solo. complex bass improv is really for a little more advanced players.