I've answered my own question. The solution is to declare multiple report tasks, like so:
- type: report
parameters:
template: traditional-html-plus
reportDir: C:\
reportFile: OWASP-ZAP-Report
reportTitle:
reportDescription:
displayReport:
risks:
- high
- medium
- low
- info
confidences:
- high
- medium
- low
- falsepositive
sections:
- type: report
parameters:
template: traditional-xml
reportDir: C:\
reportFile: OWASP-ZAP-Report
reportTitle:
reportDescription:
displayReport:
risks:
- high
- medium
- low
- info
confidences:
- high
- medium
- low
- falsepositive
sections: