Hi Peter
If you are referring to the Spectrum Spatial WMS server, then this is not able to re-project raster or imagery based data into another projection. AS John says only vector data can be re-projected.
If you are referring to adding a third-party WMS service in the SSA Admin Console, then it is possible to pick from one of the projections supported by the WMS service’s capabilities file. SSA however has a requirement that the projection you choose be the same as that of other base maps or other WMS services that have been added.
We plan to enable support for client side on-the-fly re-projection of imagery based data such as WMS, Bing maps etc in a future release of SSA, since Openlayers now supports this. I am hopeful we can achieve this in 13.0. It will allow you to add both Spectrum or third party data in its original projection.