Is there scientific evidence supporting the Enneagram?

Yes, many peer-reviewed academic studies have supported the validity and applicability of the Enneagram across different use cases:

In a 2004 study, Newgent et. al. found significant correlations between the nine Enneagram types, as categorized by the Riso-Hudson Enneagram Type Indicator (RHETI) test, and the Big Five personality traits of Neuroticism, Extraversion, Conscientiousness, Openness to Experience, and Agreeableness.
In 2005, Brown and Bartram found that the Enneagram types had predictable and strong associations to the Big Five traits, making it possible to classify 70-75% of people accurately.
In 2011, Scott found that the Enneagram’s nine personality types were consistent across sex and were unaffected by whether participants already knew their type before the study.
In 2013, Sutton et. al. examined the use of the Enneagram in the workplace and concluded that it predicted job-related variables and was a useful typology for understanding individuals’ behavior at work.
In 2018, Matise examined correlations between the Enneagram and well-known psychiatric tools, including the criteria for mental disorders in the Diagnostic and Statistical Manual-IV, using patient case studies to demonstrate effectiveness.