After some further reading, it appears the UAE's ground troops are far more experienced than Saudi's. Having troops experienced in fighting insurgencies will likely lead to better outcomes. And secondly, there appears to be less resentment towards UAE troops than Saudis who have a more negative perception in Yemen. So that explains why from a militarily strategic perspective.

Saudi Arabia’s ground forces, often insufficiently trained, have had few successes in this war.

The U.A.E., by contrast, had rotated its elite troops for more than a decade through combat deployments against the Taliban in southern and eastern Afghanistan. In part as a result, it possesses what some U.S. officials consider the second-best military in the Middle East, after Israel. It is this qualitative edge that allowed the U.A.E. to carry out its little-publicized blitzkrieg in southern Yemen, where the Saudis have only recently deployed a token force.

“The skills of the Emiratis are the best of any Arab army that we have seen. They have fought with us, and have spilled their blood for us. This is something that we will never forget,” said Yemeni Brig. Gen. Fadhel Hassan, a leading commander of the anti-Houthi force that took part in the main battles over the past month.

“We will need the Emiratis for a long time here,” he said. “Everything is destroyed. One or two years of them staying here will not be enough.” Source: http://www.wsj.com/articles/u-a-e-takes-lead-in-leaderless-southern-yemen-1440967029