So after you peal away a layer or two of buzz words...
What are these guys good at?
I don't know, exactly, but, in general, software defined networking has been viewed as an important next step in the development of "internet scale" computing.
You can look at Google's approach to datacenter and internet service design as being the exemplar of earlier phases of this progression. Google created their datacenter around building blocks made from commodity motherboards and storage, rather than specialized limited production high end servers. Robustness and redundancy was tacked at the software and networking layers. Since then, this same approach has been embraced to varying degrees by Microsoft, Amazon, Facebook and others.
Up until recently though, all those commodity based servers were tied together using proprietary networking gear, much of it from Cisco. Software defined networking is an effort to apply the combination of commodity hardware and tailored software to datacenter networking. They are generally using commodity routing and switching chips, controlled though software running on linux.
I am certain that Amazon, Google, Facebook, and probably Microsoft already have teams working on their own internal software defined networking initiatives. I don't know what Apple has been doing to date, but it sounds like they acquired an experienced team to give their efforts a boost.
I don't follow Apple's datacenter efforts closely, but when I last looked, it seemed like Apple was more apt to buy solutions datacenter hardware, systems, and even cloud services from other vendors. Google, Facebook, Amazon, and probably even Microsoft have been more likely to do at least the software themselves. This might hint at a shift in strategy.