What are those Blue Nike logo / Check sign with a + sign

"Check" +

What are does during the cutins of play highlights

Its a Nike + replay specific for players wearing Nike shoes. Nike + is a workout brand thing, so yea, its just advertising/special replay that doesn't turn off if you have auto replays set to never

Nike+ is a system Nike designed to track your stats while you train or play. In this case, they will tell you how high the player jumped to make the dunk (probably random though).