If you're using a recent version of SWPM, it shouldn't be a problem to run it while logged in as the sidadm user. In fact, this is how I pretty much always do it.
But, you should check that sidadm has the privileges required -- to run SWPM it should be a local administrator. When you installed SQL Server 2012, did you set local Administrators to be in the sysadmin role in SQL Server?
Cheers,
Matt