Except for Microsoft Visio which is the obvious choice for creating .vss stencils, you can also find some dedicated converters like the PNG2VSS which can produce a MS Visio stencils from a huge variety of both bitmap and vector formats, including SVG.
Convert XML based scalable vector graphics format to Microsoft Visio smartshapes data.
We found 2 software records in the database related to .svg to .vss file format conversion.
Microsoft Windows software - convert svg to vss on Windows
A vector based diagramming software from Microsoft
Convert from svg file format
The tables with software actions are a good pointer for what a certain program does with various file types and often may give users a good hint how to perform certain file conversion, for example the above-mentioned svg to vss. However, it is not perfect and sometimes can show results which are not really usable because of how certain programs work with files and the possible conversion is thus actually not possible at all.
A converter for MS Visio stencils