A summoned FallingSand entity will not appear. Using the this command show, of the most simplest variety, /summon FallingSand ~ ~50 ~

will summon the FallingSand but it will not be visible and is not considered an entity in the F3 statistics screen. This Invisible entity will still though set a sand block when it stops falling.
If a normal sand or red sand or gravel block is set and falls it will show the cosponsoring FallingSand entity. Very strange.