At Dartmouth. Greek life dominates. You can “not” go Greek and be in the minority. You can even thrive from being in the minority. But Geek life is very strong and in past years has had to be reined in by the administration (ie., Greek parties on Thursdays made Friday classes basically dead and it became to prevalent with enough professors abdicating, thinking the trend too strong, that it had to be fixed.)
On the other hand, I don’t think you’re against Greek Life, since you picked some colleges where it’s quite strong (WashU, Duke, Dartmouth).