I've installed all my Domino test and demo servers in VMs running CentOS
6.x. It's very, very similar to the officially supported RHEL 6 ("aims
to be 100% binary compatible") and I had no real issues yet.
Only one annoyance: I couldn't install the Domino server in graphics mode, only in console mode. Today I've found out why: I was missing a required package: libXp. A quick yum -y install libXp and now I can run the graphic installer. Yay!
Source: Domino 8.5 - Required Linux packages and updates