Like anything: it depends.

Do you consider propylene glycol a chemical (I mean, a BAD chemical)? Then avoid, e.g., Altadis.

Olde timey tobacconists, e.g., LJ Peretti, use "flavorings" (e.g., rum) or "additives" (e.g., deersfoot), but not chemicals per se.

What's nice about blenders is that while they might not give you the exact ingredients, they often WILL divulge some of their techniques and sources. Lemme see if I can find the nifty pipe tobacco university site... hold on...