I don't think this is correct. I have many alerts in place that are based on calculated metrics. The issue I have, however, is the Adobe-provided calculated metrics do not show as available options (i.e., only custom calculated metrics are available for selection).
Given that alerts now supports calculated metrics, it would be nice if the Adobe-provided calculated metrics (e.g. Revenue / Visits, Conversion Rate, etc.) could be selected. Being unable to do this, I'll need to create my own versions of these "standard" calculated metrics, which creates unnecessary duplication.