I realize this is an old thread, but I've been playing in big-bands for years, and have some thoughts about this. Charts vary a lot in terms of the arranger's intentions and the importance of "playing the ink."
I tend to take the arrangement at face value, and play the ink if it's notated, for several reasons. First, it's interesting to play something that's not just me on autopilot. Second, a lot of the older material loses its character if you try to modernize the bass line. Third, I get plenty of chances to improvise bass lines at my combo gigs, and I appreciate a chance to keep my reading chops up to date. Practicing at home, I treat the lines as mini-etudes -- again because they force me out of taking the path of least resistance on tricky passages.
Some written parts look like a lot of thought went into them, or the arranger was crazy, or both. My band has played some Gerry Mulligan arrangements where I can't grasp the harmonic concept of the bass part at all, and I finally "got it" when someone who was subbing for me penciled the changes in. I'm pretty sure the Kenton bass parts are all deliberate, and cool. He liked unisons of all the bass instruments.
There are some charts that were obviously not arranged with so much care, such as "some dance band leader's transcription." Sometimes I get the sense that they wrote notes in case the bassist of the night couldn't read changes. (This is particularly noticeable when someone has written the note names above each note).
If you're a student, the chance to work on both kinds of reading chops is a huge benefit of playing in a big-band.