For those who don't know better, the dogs are mostly there to provide dumb people a (false) sense of security, and the ill-defined "drug dance" that is supposed to be a lawful "alert" is just a scheme for cops to circumvent the 4th Amendment.
(I've seen Customs officers take the stand to define the "drug dance" and it's obvious they're just confabulating, and the courts are too complicit in the whole Drug War/Terrorism mania industry to end this.)
Ingredients for bombs vary considerably (not some magic 'unique' scent)and masked with perfumes etc there's no way dogs would smell them in a moving target. Drugs other than marijuana are most often odorless, and non-volatile, so those too are not something dogs are going to detect, especially if masked. But if they want to escalate the whole Security Theater charade, more power to 'em.
After all, they don't have much else to do these days.