Stored procedure calls are "written" in the db management system that you
use. Visio has no native ability to "call" an SPC, it has to be done via
code that somebody develops. The normal v2007 Pro data connect process can
access both Tables/Cubes. The interesting part is that in the connect
process it lists Views as Tables (which obviously infers that you might take
advantage of the underlying query definition for custom data scenarios). If
you're willing to be adventurous you might investigate how the data
connectivity is accomplished using the ODC connect file, which is stored as
XML and editable.
al