Have you followed the steps at: https://docs.imperva.com/bundle/v14.14-database-activity-monitoring-user-guide/page/2493.htm ?
It's been quite a while since I configured sending traffic to ArcSight, but I expect that ArcSight still works essentially the same. The basic integration steps on the Imperva side are still the same for DAM. Data Security Fabric (DFS) would be a bit different.
If you need to make any adjustments, you might want to reference this article, and the associated/linked articles in the same "placeholders" section/chapter of the documentation:
https://docs.imperva.com/bundle/v14.14-database-activity-monitoring-user-guide/page/3680.htm
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John Thompson
Presales Director
Imperva
San Diego CA
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