Looking at the images under Syntax here.
It shows the syntax (grammar) in a visual way. Is there specialized software for creating and editing such diagrams?
See Tool for generating railroad diagram on StackOverflow.
There is an online railroad diagram generator which generates SVG diagrams from EBNF
Some web searching for "syntax diagram generator" (and similar phrases) got me this: http://karmin.ch/ebnf/index
I've never used it but it looks like it will generate syntax diagrams. They won't look 100% like Oracle's but they should still be usable. I don't know what tool Oracles, uses. Probably some internal tool that they don't distribute.
Here's another one: