LaTeX compiation tools such
rubber, etc are not needed for ConTeXt.
In LaTeX, the basic commands such as
luatatex just run the underlying TeX engine with LaTeX format pre-loaded. Features such as bibliography, index, glossary, etc are handled by external tools, and it is the responsibility of the user to run these tools. Furthermore, it is up to the user to run LaTeX appropriate number of times to get the cross-references etc right.
In contrast, in ConTeXt the basic commands
texexec are wrappers around scripts written in lua and ruby respectively that take care of everything. Sorting of indexes and glossaries are handled the ConTeXt format, and the wrapper scripts run bibtex if needed and also compile the file as many times as needed.
Coming back to the question at hand, there is no need for a context rule for arara.