Can't create reports utilizing a non-synced record type

You should be able to use any kind of data. Can you share a code sample?

The following is the chart I am trying to add in my interface: 

a!sectionLayout(
    label: "Section",
    contents: {
      a!pieChartField(
        data: 'recordType!ED_Dispute_Copy',
        label: "Pie Chart",
        labelPosition: "ABOVE",
        allowImageDownload: true,
        colorScheme: "RAINFOREST",
        style: "DONUT",
        seriesLabelStyle: "ON_CHART",
        height: "MEDIUM",
        refreshAfter: "RECORD_ACTION"
      )
    }
  ),

and this is the error I am getting at the moment: 

Interface Definition: Expression evaluation error at function a!pieChartField 
[line 18]: The source record type ED_Dispute_Copy in Pie Chart [label="Pie Chart"] is invalid. 
Only synced record types or record types backed by a data store can be used as the data source
for a chart.

You can feed any data to charts. Just do your query, and create a list of chartSeries.

a!pieChartField(
  label: "Opportunity Sources",
  instructions: "Leads are calculated based on the initial mode of contact",
  series: {
    a!chartSeries(label: "Existing Client", data: 12),
    a!chartSeries(label: "Inbound Call",    data:  6),
    a!chartSeries(label: "Tradeshow",       data:  8),
    a!chartSeries(label: "Web Site",        data:  6),
    a!chartSeries(label: "Referral",        data:  7)
  },
  colorScheme: "MIDNIGHT",
  showDataLabels: true,
  showTooltips: true,
  showAsPercentage: true
)

https://docs.appian.com/suite/help/23.4/Pie_Chart_Component.html#pie-chart-with-label,-instructions,-data-labels,-tooltips,-and-percentage