The Multiple SCMs plugin was a great idea, unfortunately it doesn't work quite yet with StarTeam. I setup a test system with the latest Jenkins (1.502), the Multiple SCMs and StarTeam plugins and tried to build a test project. Several problems exist
1) the Multiple SCMs plugin looses it's configuration when re-entering the Projects Config page. So you type the config in, apply the changes and save. Kick off a build and it checks out the files. Open the projects config page again and the StarTeam configuration fields are all empty.
2) all SCM's check out into the root of the workspace. E.g. I have two instances of the StarTeam plugin. The paths to the different folders in StarTeam are Suite\ToolA and \Suite\ToolB. Expected would be that the files are checked out into %WORKSPACE%\Suite\ToolA and %WORKSPACE%\Suite\ToolB or at least %WORKSPACE%\ToolA and %WORKSPACE%\ToolB. But they are all checked out into %WORKSPACE% directly.
3) Files that are not in the view of the current SCM will be deleted during checkout. Meaning if you have two StarTeam SCMs (using the example from above) and checkout Suite\ToolA, it'll delete all files that belong to Suite\ToolB because they are not in the View of Suite\ToolA. When it is done with the first SCM, it will start checking out all files from Suite\ToolB and this time around delete all files that it previously checked out for Suite\ToolA.
It would be awesome if you could find a way to fix those things and make the StarTeam plugin compatible with the Multiple SCM's plugin. Maybe just an added job configuration option that says always cleanup workspace (enable/disable). And maybe specifying the root folder for the checkout, with the default of %WORKSPACE%\<Starteam Folder name> or so.
Thanks for the quick response btw 
Sandra
The Multi-folder checkout feature was not folded to the trunk.
It should probably be a separate and repeatable plugin option allowing separate configurations.