Sure. Some clients prefer us to use Linux, since their teams large or small are comfortable with it. OpenBSD is still a rather esoteric OS for most. I've been using both since 1998, so I can go either way. RedHat/CentOS offer support for 10 years is high up on the totem pole for me and plenty of others. OpenBSD releases every 6 months like most Linux distros, so some mission-critical users are uncomfortable with this pace, and I cannot say I blame them.

SELinux is great for areas that are into DAC/MAC/RBAC, plus the aforementioned lengthy support. I see more and more customers wanting Red Hat/CentOS than any other Linux distro and for good reason. It just works. Things like CPanel only run on these distros. Red Hat/CentOS are also very predictable and they offer superb documentation. More and more people are uncomfortable with things like Debian because there is no throat to choke if they need support or if something goes pear shaped.

I have worked on Linux for 20 years now and I have never, ever seen Debian or Slackware or even Ubuntu in a TRULY mission-critical role. People may disagree, but there are reasons why Red Hat/CentOS are chosen. They are typically very stable, use tested software, and are well documented for the use cases they excel in. Red Hat runs some truly mission critical stuff like power grids, and more and more SCADA systems, now that they are being upgraded due to threats.