No, sadly:
The Excel 2010 client application does not support co-authoring workbooks in SharePoint Server 2010. However, the Excel client application does support non-real-time co-authoring workbooks stored locally or on network (UNC) paths by using the Shared Workbook feature. Co-authoring workbooks in SharePoint is supported by using the Microsoft Excel Web App, included with Office Web Apps
From Co-authoring overview (SharePoint Server 2010)
...and not for SharePoint 2013 either. Though it works for pretty much all other Office documents. Go figure.