I think that the paper already makes a good case for deploying a network edge element to facilitate secure traversal of UC signaling and media. So I guess this question is related to the differentiation of a UC vendor-provided element (such as those provided by Siemens, Microsoft and Cisco) vs. a 3rd party provided element (e.g. NET, Acme Packet, Ingate, Edgewater Networks, AudioCodes, etc.)
(If I have misinterpreted this question, please let me know).
The UC vendor elements are typically focused on the specific needs of those applications. So while they will do a great job of providing DMZ traversal of their own UC traffic at scale, they won't handle generic traffic, such as arbitrary data streams from application servers. On the upside, they are a lot cheaper (i.e. tending towards $0 excluding hardware) than a 3rd party element. Some of these elements (specifically those from Microsoft and Cisco) support inter-enterprise federation between same-vendor solutions, significantly reducing collaboration costs and increasing the utility of UC deployments and this is not (yet) a feature of the 3rd party E-SBCs.
The 3rd party E-SBC elements are designed to handle all kinds of IP traffic, including UC traffic from multiple vendors as well as web/app server transactions and data streams. The multiple UC vendor scenario will soon become an issue just as enterprises found themselves owning 2 or more brands of PBX. So, viewed across the range of requirements, you may need to deploy an E-SBC in any case, thus invalidating the element-cost argument of the vendor specific solution.
There is a case to be made that the 3rd party products are more secure than the UC vendor elements because they are provided by vendors who 'do security for a living'. This argument has some merit, but I am not sure that I completely buy it: the UC vendors greatly reduce their attack surface by focusing purely on their own traffic. I have yet to hear of a UC vendor solution that has been compromised or shut down by malicious attack (I may live to regret that statement); however we read almost daily of data theft from and compromises of more general commercial and government systems.
The bottom line is the need for some form of robust network edge security. Each enterprise has a range of requirements and all factors must be weighed by the UC/network administrators in defining their solution.