Hi All, I am looking to use Apache Pinot for Fraud detection and prevention. Has anyone used Pinot to power such use case?

Yes, very common. More info on that use case can be found here https://dev.startree.ai/docs/startree-enterprise-edition/startree-thirdeye/

Possible to use it in customer journey with sub-milisecond latency?

For threshold based alerting, shouldn't be an issue. But I'll defer to the experts to comment on that.