Regarding pre-emergent, I think it is fine to skip it so you can overseed. Really, I think it's too late anyway for per-emergent only. Last year I worked on a baseball field renovation that had heavy crabgrass pressure and used Tupersan (Siduron) in mid-August to buy a window of a few weeks to get the grass germinated. That worked pretty well. The soil had been turned completely on that one.
This is the first year I have used pre-em on this soccer field. Other years I held off because I was concerned about germinating seed in the divot mix and overseeding goals through the girls (spring) season. I have learned that the girls do not damage the field nearly as much as the boys do, so less overseeding is needed. I now pre-germinate seed in some of the topdressing mix in buckets or an old wheelbarrow if I need it in spring.
This field has a pretty good stand of grass. I do not feel a big threat from crabgrass and do not care for nitrogen that early in the year. In looking at the bigger picture, though, I know that I plan to stress this field for water through June and July and did not want any thinning I may get to give crabgrass an opportunity to get established. That’s my thinking. Time will tell how it turns out.