You can get 100% EQM/MQM on DL when flying CO, but you can't purchase the "discount economy class" fares. If you purchase regular "economy class" you will get 1:1 EQM/MQM.

Discount Economy Fare classes:
Q, I, S, W, T, X, L

Economy Fare Classes:
K, M, N, B, O, V, U

I actually just flew CO from LAX-IAH-BRO-IAH-LAX and used my DL #. I was on a Y fare and got 150% MQM and was upgraded to F on my LAX-IAH leg.