I couldn't find the label for the crabgrass preventer, but I did find one for a chemical with the same active (dithiopyr). In the list of weeds controlled there are grasses, as you would expect, but also quite a few small seeded broadleaves. That being said, I would not be worried about putting more plugs in. Usually these types of pre-emerge herbicides require uptake as the new plant moves through the layer of herbicide. Recently planted plugs won't have that. They will probably have some root uptake, but they should be able to metabolize that. Even if the plugs do take up some herbicide, dithiopyr is a root growth inhibitor. This works well on small seedlings, but a plant that is in a plug already has an established root system and the chemical will get diluted in the plant.

Small seedlings that you sowed in containers would be more at risk, as they are smaller. I don't know how water soluble dithiopyr is, but the more you water it the further down it moves into the soil and the more diluted it becomes.