Zinnias? Yes, they work very well just sprinkled. Just make sure the soil in the bed is fluffy, not at all packed down.

I think it helps a lot if you have the time, energy, patience, whatever to push each one down just low enough to brush a bit of dirt over it. If I don't, the birds and/or squirrels eat most or all of my seeds, or they just bake in the sun without enough moisture to instigate sprouting. With tiny seeds, that's impractical though.

If the spot I want to grow in is mulched, I rarely have any luck without starting in pots first.