Eh, the risk of injury is pretty overblown. You could get injured at any time. They played how many games in high school? They could get hurt during off-season lifting. They could get hurt the first day of practice. Injuries happen. Skipping one game lessens that risk but by such a small amount that it's hardly worth talking about. Those guys are all pretty much headed for a redshirt anyway.
Would mean a lot more in terms of PR and goodwill that the slightly reduced risk of injury.
Yes, they played in many HS football games... 8 months prior. So if they had an injury during their HS season, the University already knew about it and actually had a chance to change their mind if they wanted to offer them a scholarship. No one wants to lose a player to injury the DAY before they report. I say DON'T let them play.