We seem to have some every year no matter what but it's better if it gets a shower a day or two after planting.  Most of our issues come when we have to get it up with soil moisture alone as some of our ground will be hard as a rock in the time it takes corn to come up, whether that's two weeks in late March or 4 days in May.  The bulk of the uneven emergence is due to field terrain and margins are all that really have any major in row discrepancies.  No yield loss in our opinion if a hill comes up 3 days after a flat.  Digging behind the planter it's not uncommon to find a seed with 1.5" of moisture above it and the next is beside a gravel that has no dry dirt within 1/2" of it, then the next is in good moisture, meaning the middle plant is gonna be a weed.  Don't know of anything that will fix that.