The scenario is that Excel files are uploaded to a folder in SP2010. When a new file is loaded, I would like to use a Workflow to call the SSIS package that processes that file into a Database and updates an SSAS Cube. I cannot see any action in the Workflow tasks or actions that will call an external process, either Powershell, win32 or Cmd ? If it is not in Workflow surely there must be some approach in Sharepoint to call an external process, to enable Interfacing?
What is the workflow doing? If its doing nothing but calling ssis then it's a little overkill since its workflowing nothing!
Why not have the ssis package run under a SQL job periodically checking for new files?
If it needs to run on upload (don't forget to cater for check out/in), an option is to call a stored procedure to execute the ssis package using xp_cmdshell. Alternatively use sp_start_job and start a job configured to run the package.
I'd use one of the above given its on a remote server? If local you could use Microsoft.SqlServer.ManagedDTS
Hope it helps.