Just tried it now..
-Created a form
-added an oleboundcontrol to it
-set control source to mytable.visio
-create a table called mytable with a general field called visio
-put the drawing in with APPEND GENERAL visio FROM GETFILE()
(picked a visio drawing..)
-ran the form and the drawing showed up...

printing ?form1.oleboundcontrol1.OleClass
returns visio.drawing.6 which should be the answer to your question.
But it seems append general from (FILE) is enough.

BR
Tim