Yes, there is a no-output option. Just set the destination file to '/dev/null'.
$ asciidoctor -o /dev/null sample.adoc
The warnings & errors will be printed to stderr.
/dev/null is a virtual directive that tells Asciidoctor to not output anything (you don't have to be on a Unix system).
If you are using the API, you can also just convert the file to a string and just not capture the result.
[source,ruby]
----
Asciidoctor.convert_file 'sample.adoc', safe: :safe, to_file: false
----
Cheers,
-Dan