Interesting point.
But true vertical integration is very rare (if not impossible) for an indie company.
Do you mean, vertical integration where EVERYTHING from straps, screws, crystals and movements is done in house?
I think that would only leave seiko and maybe Rolex?
Or do you mean vertical integration where all of the design/finishing is done in house.
I would argue, someone like HALIOS, which is a company run by 1 guy genuinely passionate about his products and designing all his watches by himself is an independent.
Certainly on a lower level to the list of indie stars regarding finishing, stock components, ETA movements, etc - but independent in spirit and direction nonetheless.
Cheers