Corys do vacum sand. I goes through their gills. That is why sometimes you will see blood worms coming out their gills. Cichlids will do the same thing. They do it a little differently of course. A Cichlid dives into the sand and grabs a mouth full then blows it out his gills.
But that is another reason that Cory philes kinda get pushy about sand. I have mixed sand and flourite. I saw where one guy in the plant section had put retainig walls and had sand on one side and EcoComplete on the other.
You know I just got two bags of flourite. I might do that sand with a retainer thing. The worst that happens is that they mix after a while. But I really don't do well with plants in sand. My Corys always dig everything up.