What Do Admission Officials Know About Applicants' High Schools?

Do colleges have access to Naviance scattergrams, or otherwise maintain their own database of past applicants from each high school, to put GPA’s/scores into context? Especially if a high school only sends a few applications to a particular college each year, will that college look at data points from past years as well?

What about colleges that say they don’t compare applicants against others from the same high school?