I'm not a fan of the cutisie "swing choir" doot-doo-doobie-doot thing. As a matter of fact, I've got a tape somewhere that someone gave me that is a compilation of bad scatting at a college jazz festival. It's funny as hell. The use of awkward/overused/jive syllables is the main thing that makes it lame IMHO.
That being said, often the best way to convey many of the concepts of jazz articulation, rhythm and swing in a rehearsal situation is by singing. When I rehearse a band I often sing specific figures (more "rhythmic" singing than "melodic" singing) and I have students sing figures to me. We've talked about this on another thread, but removing the obstacle that the instrument creates can really help to learn a jazz rhythmic concept.
It's interesting how horn players historically have borrowed from singers and vice-versa. One thing I do appreciate as an instrumentalist is when a vocal scat solo actually follows the chord changes and form. Once the vocal improvising begins, I evaluate it with the same criteria I would use for any other improvising musician. I think where I (and most instrumentalists) learn from singers is primarily in the area of phrasing, most often pertaining to ballads. And as ubu said, knowing the lyrics when performing a ballad is essential for a horn player.