VICIdial can run on any distro. True, but in my opinion best distro for servers is CentOS. That does not mean that I am considering goautodial. Which is total waste. Try vicibox instead.
VICIdial developer(s) use opensuse and recommend it. They talk about not to use CentOS for being not stable for vicidial. I have done so many installations using none other than CentOS and never faced any such issue. Most of the people who deploy vicidial use centos.
In the end it is about which distro is famous for being server focused and have a feel for that. You can tell your client that you built vicidial on vector linux. When a technical person from client company asks for distro and you tell him that you would put centos, he would quickly favor it. Ubuntu is famous but it lacks the feel for server focused distro. It may have equal share in server market as compared to CentOS but to me it is like a, like a, monkey; it would do the job but in a twisted fancy way no straight aproach.
Seriously dont use any other distro!!!