The Sketch and Toon render settings are stored in the related video post, not the render data.
The video posts are stored in a list, the first element of that list can be obtained with
GetFirstVideoPost() on the associated render data.
Then loop trough all video posts simply with
GetNext() and check the type of the current video post.
Here is some code:
rd = doc.GetActiveRenderData()
if rd is None:
vpost = rd.GetFirstVideoPost()
if vpost is None:
found = False
found = vpost.GetType() == 1011015
print "Found S&T VideoPost"
vpost = vpost.GetNext()