When you have BarSeries and LineSeries in RadChartView the problem is that the DataPoint.Presenter is always BarSerries, never LineSeries. 

To workaround, create custom renderer:

this.radChartView1.CreateRenderer += this.RadChartView1_CreateRenderer;
private void RadChartView1_CreateRenderer(object sender, ChartViewCreateRendererEventArgs e)
{
    e.Renderer = new CustomCartesianRenderer(e.Area as CartesianArea);
}

public class CustomCartesianRenderer : CartesianRenderer
{
    public CustomCartesianRenderer(CartesianArea area)
        : base(area)
    { }
    public override DataPoint HitTest(int x, int y)
    {
        for (int i = this.DrawParts.Count - 1; i >= 0; i--)
        {
            DataPoint dataPoint = this.DrawParts[i].HitTest(new Point(x, y));
            if (dataPoint != null)
            {
                return dataPoint;
            }
        }

        return base.HitTest(x, y);
    }
}