I can't seem to find this addressed anywhere, though my Google-fu isn't quite what it used to be.
The main feature of a Herb Witch is Herb Lore (Ex), which does a few really neat (imo) things including making use of Profession (herbalist).
Herb witches are masters of herbalism, and can use their herbs to duplicate many of the effects of alchemy, as well as craft tinctures of their own. An herb witch can attempt a Profession (herbalist) check in place of any Craft (alchemy) check and gains a bonus on Profession (herbalist) checks equal to half her class level.
Alright, pretty straight forward.
The archetype also forces you to take the Cauldron hex at second level. Again, pretty straight forward.
So, here's where I cringe a bit: the Cauldron hex grants an insight bonus to Craft (alchemy), which is essentially replaced by Profession (herbalist) for Herb Witches.
I get that Cauldron still gives a feat (Brew Potion, for those unfamiliar with it), but it also means you're getting forced into a hex you can only partially utilize. While I definitely like fluff of it all, I do hate being forced into something I can only partly use.
Am I missing something somewhere? Or is this worded as intended?
If I had a player approach me with this archetype, I would allow them to apply the +4 from the Cauldron Hex as a bonus for crafting alchemical items using Profession (herbalist). I would not add it to their Profession (herbalist) for the other benefits of herb lore.
RAW, I think you're stuck with a +4 to Craft (alchemy).