That amount of residue shouldn't be a problem for a good NT drill. You said 'warm season mix', I'm assuming you're talking warm season perennials like switchgrass or big bluestem, not a warm season annual like sorghum sudangrass. Warm season perennials are notoriously slow to establish, like a couple of years before you have a decent stand. I'd be afraid that without a burndown, the cool season stuff will comeback when it cools off and outcompete the warm season stuff.
Also note that the warm season grass seeds can be big and fluffy, they don't work well in many grass seed boxes without an agitator to keep them from bridging in the box. Some folks will mix them with a small amount of oats or fertilizer and seed it that way.
But that's based on my experiences here in Pa. Your neck of the woods is different than mine, I'd talk to someone with local knowledge of planting warm season grasses.
Dale
