I don't think that there any rules at all on what can/should be smoked in particular pipes. However, "I" prefer certain chamber shapes for specific tobaccos. The outside shape is for pure aesthetics in my opinion.
For myself, I prefer a tall stacked chamber and dublins for my Va and VaPer blends, because I like the way they stove in the pipe giving me a change in taste as the bowl progresses, and pots and larger chambers for mixes, and small chambers for my darker, stronger blends.