Hello,
After diving into the www, I don't have a clue about the support of vectorial grahics/image by reporting services. It seems to be impossible. We are using Reporting Services with a PDF rendering and we are forced to use raw bitmap into reports. That leads to huge sized reports. We know that dealing with vectorial graphics will help but such feature seems to be not supported by reporting services.
Custom reports items have much different case than native report items. They are generated during report rendering, which means it is possible for us to vary both the type (raster or vector) and the DPI of the image based on the developer needed (rendering form). For example, we currently use 300 DPI raster for PDF, vector for print and Winforms and 96 DPI raster for HTML and Excel. Custom Report Items, on the other hand, are generated during processing. This means only raster images can be used (since they must work with all renderers, including those which do not support vector images) and only a single DPI can be chosen for all rendering targets.
Custom Report Items should have to generate a raster image of sufficiently high DPI as to be high quality when printed. A default setting of 300 DPI should be sufficient for most applications. However, since the renderers don't currently pay attention to DPI, this will result in the image being three times the intended size. You need to set the sizing property with fitting proporational.
m_MyImage.Sizing = Microsoft.ReportingServices.ReportRendering.Image.Sizings.FitProportional;
There have been problems in the past with SQL Reporting Services and PDF compression. If you are creating serverreports in a version prior to 2005 or localreports in a version prior to 2008 the hugh pdf files could be caused by the compression issue.
No, there are no known ways to insert vector graphics within SQL Reporting Services. Now since RDL 2.0 some support for HTML is supported but I'm not sure if that would include VML or anything adequate for showing graphics.
I've basically have the same need and have been communicating as much as possible with those involved in SQL Reporting Services and other RDL based alternatives such as DataDynamic Reports and FYI Reporting to see if I can get this type of support. So far DataDynamics Reports support people claim to have "better EMF and CRI support" but the others have no such capabilities nor do they have any publicly known plans to implement them.
For more information see my post on the MSDN forums regarding whether OLE object or EMF image support would be introduced in any future versions of SQL Server Reporting Services.
As for those who may be willing to implement a solution themselves I think balaweblog is right in that a custom report item could be created to render vector graphic in your preferred format, but that requires that you basically write the control that isn't supplied by Microsoft and write a rendering engine if your format isn't directly supported on the system or in the .NET Framework for example (SVG comes to mind).
Update: It appears somebody else also is looking to implement vector graphics in FYI Reporting however they seem to be running into the same roadblock that many have when trying to export to PDF.