No, Van Dorn cost Grant a lot of time, and forced him to gave up invading central Mississippi. His loss against Van Dorn, was the first clear victory for the Confederates in the west.

No, I mean Halleck, the true innovator in the art of living off the land and not the supply line. He ordered Grant to give up his supply lines and forage from the land in North Mississippi in order to speed up the campaign, Grant poo-pooed the idea as impossible and refused to do it. Later Grant somehow remembered the order and used this to quickly get around Vicksburg. Sherman used this tactic against Meridian. Halleck had some very good ideas.

Grant was somewhere in a tent when his forces were needed at Iuka. Iuka was not a true Union victory, since Price attained his goal of taking the town and its supplies, was ordered out of the area before the battle began, was not destroyed, and was not stopped from joining Van Dorn.
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David Upton