Sure you can, please use the ArrayDataSource like following;

class MyReport extends \koolreport\KoolReport
{
    function settings()
    {
        return array(
            "dataSources"=>array(
                "apiarray"=>array(
                    "class"=>'\koolreport\datasources\ArrayDataSource',
                    "dataFormat"=>"associate",        
                )
            )
        )
    }
    function setup()
    {
        //Connect to your api here and load json, parse json string to array and
        //store the data in the associate format like below:
        // $data = array(
        //     array("customerName"=>"Johny Deep","dollar_sales"=>100),
        //     array("customerName"=>"Angelina Jolie","dollar_sales"=>200),
        //     array("customerName"=>"Brad Pitt","dollar_sales"=>200),
        //     array("customerName"=>"Nocole Kidman","dollar_sales"=>100),
        // )

        $this->src("apiarray")->load($data)
        ->pipe(...)
        ...
        -.pipe($this->dataStore("result"));
    }
}

For example you have a SaleByMonth report which is of course return total sale by month. You can make the api like this:

https://www.example.com/api/salereport?type=month

And then you can do:

if($_GET("type")=="month")
{
    $report = new SaleByMonth;
    $report->run();
    echo $report->dataStore("result")->toJson();
}