I can't speak to plantuml support, but Zim was--guessing here--one of the first to visualize links. Look at the plugin "Link Map." Been using it long before the current crop of markdown knowledge gardens came about.
I did install it, but it's much more clunky. It doesn't update live, it opens in the browser instead of zim and after a while i figured out it didn't show everything, but stopped a about 5 nodes from the main current one. The graph is also pretty ugly.
Maybe they improved it since, but the Zim graphing capabilities just didn't even compare to foam's last time I tried it.
Maybe they improved it since, but the Zim graphing capabilities just didn't even compare to foam's last time I tried it.