Can an ophthalmologist actually see vitreous syneresis in a dilated pupil exam?

Absolutely! Sometimes we don't even need to dilate the pupil to see it. The decomposition of the vitreous that often occurs in later life allows the matrix-like fibers of the vitreous to be seen in their various forms: specks, clumps of lint, a gauzy "curtain," and other whimsical shapes. These will typically "slosh" around" as the eye looks in different directions.