Yes, you can reference a column in your AI prompt without making it required to run. In the Prompt Editor, there's a Required to Run toggle next to each referenced field. You can leave this toggle disabled for columns you want to reference but don't need to be populated for the prompt to execute.
When Required to Run is disabled, the AI enrichment will still run even if that referenced column is empty, but when enabled, the enrichment will be skipped if the field doesn't contain a value.