I can't speak to how common that sort of custom tooling is in the industry, but as to whether it was necessary the article already explains that pretty clearly:
> The current process for building a pressure dome takes about a week; 1 or 2 days to tack up and fit steel sheets, 4 days to weld the sheets together, and 1 to 2 days for X-ray inspections and repairs.
> [...]
> The knuckle seamer looks something like a giant zipper that articulates over the front and back of a dome, like a taco shell around its filling. [...] Then, in about 10 minutes, an automated torch will trace down the length of the curve, providing a precise weld. Following this, the dome is rotated to bring the next seam into view.
> [...]
> With this new X-ray machine, SpaceX hopes to compress a process that can take a day down to a few hours.
So the new machines reduce the amount of time needed to weld and inspect a pressure dome from several days to several hours. I'm certainly no expert, but that seems like a pretty big deal to me.
> The current process for building a pressure dome takes about a week; 1 or 2 days to tack up and fit steel sheets, 4 days to weld the sheets together, and 1 to 2 days for X-ray inspections and repairs.
> [...]
> The knuckle seamer looks something like a giant zipper that articulates over the front and back of a dome, like a taco shell around its filling. [...] Then, in about 10 minutes, an automated torch will trace down the length of the curve, providing a precise weld. Following this, the dome is rotated to bring the next seam into view.
> [...]
> With this new X-ray machine, SpaceX hopes to compress a process that can take a day down to a few hours.
So the new machines reduce the amount of time needed to weld and inspect a pressure dome from several days to several hours. I'm certainly no expert, but that seems like a pretty big deal to me.