This might be what they mean above, but for the zest I would soak it in alcohol and then either add the whole tincture or strain out the zest and add the alcohol. You can dose to taste at packaging. This is also a good way to make citrus vodka if you are so inclined.
For the chamomile, I would boil it and make a tea and do the same as above. You could add the tea to the fermenter without worrying much, but getting the dose right could be a pain and you'd have to taste it frequently to rack it when the level hits what you want.
Agreed on both parts here.
With any material added in secondary, the tincture is a great alternative to adding the raw ingredient. You can dose to taste, you don't have to worry about contact time in the finished beer, and you reduce risk of extracting unwanted flavors.
Ever since ruining a batch of Christmas beer with a boquet garni in the keg, I've stuck to a tincture for spices, citrus zest, and herbs. The only thing I haven't tried is hops!