Guess I am a bit confused by the question
A sparse column must be nullable and cannot have the ROWGUIDCOL or IDENTITY properties. A sparse column cannot be of the following data types: text, ntext, image, timestamp, user-defined data type, geometry, or geography; or have the FILESTREAM attribute.
I'm not sure how something is "defined on them", it may have had a meaning different than the one I read into it. It is clear that a Sparse Column cannot have a Filestream attribute.
There have been times in the past when my sparse sql skills prompted me to look at a Union statement when trying to compare two values that would have best been seen in a left join. The sparse column would have come in handy. It is a good topic. I wonder if we can just reword it slightly... maybe "Can a sparse column have a FileStream Attibute?"