The evaluations are subjective with the exception of the top 200 or so who have attended a camp and competed without pads against peers. They typically have 40 times, bench press and similar drills to the NFL combine. The top 200 outperform their peers who attend other camps. The process usually works like this:
Sophomores who have good pub will be viewed on film. If they are aggressive, or in the south near a camp site between their sophomore and junior years, they will go to the Nike camps or one of the Rivals eval camps, where they will be evaluated against other kids their age. This is one reason kids in Minnesota and Wisconsin typically don't have ratings, is that the only camp is in Chicago area. Michigan is similar with 1 camp in Detroit. Contrast those camps to Dallas, LA, Miami etc, which typically have 2 or more camps.
Junior year game film becomes a big thing. If a kid is dominant in junior game film and had good camp , they typically will get a big rating. Most offers come junior camp season and the "player rankings" are based on the junior year tape plus junior year camps. The performance in the sophomore camps plus junior year film are the biggest basis for player ratings of the top 200 players.
Senior year. The struggle, and the hole in the system, is the kid who develops late i.e. late junior year and junior-senior summer, who then blows up as a senior. Those kids are not highly rated because the Rivals/247 system doesn't really re-rate until the end of senior year. There are some coaches who hold back a bunch of scholarships until late senior year for this reason. The reason is you are evaluating a more finished product then the kids after junior year. ****My opinion. This is why some of the NFL draft picks are not top recruits. They are late developers who don't get offered until late in the process. I have zero stats to base this on, just an opinion****
The evaluators at Rivals and 247 typically have had some small school college experience as coaches or high level high school. To my knowledge, none of them are former pro scouts and only a couple coached D1 football. That said, it doesn't mean they don't know what they are doing. The challenge for players who are not top 200, or don't go to the camps, is that the "evaluator" might be a local guy who knows someone at rivals. He alerts them to the player and they view some highlight tape (i.e. Hudl) The evaluators then give them some ranking. The rivals camps are effectively pay to play, where you attend and get a ranking
For example, Josh Helmholdt of Rivals played at Grand Valley State(was a 2nd string player), then became the recruiting guru for The Wolverine Magazine and now Midwest recruiting analyst for Rivals. He has never coached at all nor played above Division 3.
Mike Farrell, the top dog at 247, is considered a top recruiting analyst, never eve played college football at all while attending Central Connecticut State. He started evaluating as a college kid as Rivals and rode the train to become the top recruiting analyst in the country.
It doesn’t mean these guys are not smart and can’t evaluate given that they are doing it every day, but I don’t think Nick Saban is bringing them in to become his chief talent evaluators at Alabama if that is what you are wondering.