I don't see what they could possibly add to the pipe tobacco except honey and perhaps some other casings for aromatics. I'm not as sure about pipes though. With meerschaums there's the beeswax of course, and with briars I guess there's a variety of possibilities (stain, lacquer, possibly some freak pre-carbonisations, perhaps buffing/polishing compounds?)... From what I remember leather dye or something similar is quite common, is that right? I think they're aniline/azo dyes, which I think are okay. No idea about the rest, but scarface's comment about shellac is worrying.
I've only smoked occasionally since I became vegan three years ago and haven't bought any new pipes so haven't needed to worry about it. Thanks for this thread though, and perfect timing since I just started coming back to pipe smoking more actively