Not a perfect science, but it would be foolish to think that talent evaluators are so bad that star ratings are basically a crapshoot. The correlation between recruiting classes and performance on the field seems pretty clear. 247 Sports actually did a study on this and looked at the likelihood of being drafted by star rating:
2016/17 Class Averages – 247Sports Composite
Five-star: 30 (62.3%)
Four-star: 311 (23.5%)
Three-star: 1,831 (6%)
Two-Star: 1,949 (1.6%)
Seems like a pretty strong correlation to me.