yea it seems like Clostridium are not killed by alcohol very easily. C. difficile spores aren't killed at all by alcohol hand wipes. Ethanol is actually a method of isolating Clostridium spp in the lab since it kills everything else so all you're left with are Clostridium spores.
So the main thing is to clean what you're using really well. Most vegetables from the garden used in canning have C. botulinum spores on them since htey're naturally present in the environment, you just make sure you scrub everything really well.
oh and to answer your question: yes, the alcohol will keep them from growing since they won't be able to live in their vegetative state (which is required for growth), but any present as spores might not be killed (although being in 96% alcohol for a long time, there's a good chance they will be).
But just wash what you're using and I wouldn't be worried about it.
Well the spores themselves are harmless, but when people get botulism a lot of the time it's from eating the spores. botulinum are strict anaerobes, so the won't grow with any oxygen present at all and if there is they go into their dormant stage (spores). then when someone ingests the spores and they pass into your gut into a prime anoxic environment full of nutrients they become active and start growing and release the toxin.
But seriously, I wouldn't worry about it so long as you wash your herbs well. If you're worried then do some research on the mortality of Clostridium in ethanol. Google scholar.
See this type of reply worries me. Should I be pasteurizing the bottles? I'm using fresh herbs so they'll leek some water, the end result is still most likely going to be over 95%, based on what i've read alcohol inhibits the formation of the toxin and that it is incredibly unlikely that a healthy adult develops botulism from ingesting the spores. Or am I missing something?