i dont know how many scouts were there yesterday, but....
from what i know of the nfl, scouts go and check out every school that plays football. now there may not be a gaggle of scouts from each team, but usually there are scouts from one of the scouting organizations.
for those who don't know, each team has area and national scouts. and then there is an outside scouting organization that most teams use to supplement their own information.
if they come across a player that intrigues them, they sometimes invite them to work out at pro days at bigger schools.