Thanks. Read up on their FAQ and they agree ... no impact on the
clover since it only restricts seed germination.

5. What weeds is it most effective controlling? What about clover?

99.9% of all broad leaf weed seeds will not germinate (grass seed
germination is inhibited as well, see below). The most common pesky
weeds that corn gluten meal controls is CRAB GRASS, CHICK WEED, and
DANDELIONS. It will NOT have any effect on clover, as clover grows
and spreads from its root system. Clover does not flower and drop seed
buds, so it cannot be controlled by a pre-emergent herbicide.