My take is that the overall rating is nice for public consumption, but means little in the eyes of a recruiter. The raw numbers and written evaluations carry weight, but that rating # is just eye candy.
Agree somewhat with Roothog. As to OP Question, yes there have been students with low ratings who have gone on to play D1. The rating may have come when the player was young and hasn't been to PG events/showcases last 2-3 years before graduation. I also know of a pitcher/hitter who is playing D1(multiple offers- one ACC,all state in HS) who doesn't have a PG rating.
In researching schools with my son, we've found quite a few players, especially pitchers, who are playing for D1 schools and don't have a PG rating at all. A few have pages on PG with some stats, but no rating. However, a lot do not show up on the PG site at all. I was a little surprised that there were so many.