I thought about using it for a big Hadoop cluster due to ZFS and jails but at that time there was no recent Hadoop port and some tinkering is often required to get rid of glibc specifics or dependencies on Linux only APIs (epoll and stuff like that)
https://svnweb.freebsd.org/ports/head/devel/hadoop2/files/
However I guess even with a good working port it's difficult to convince a team that only uses Linux for like their whole life. We somehow decided on btrfs at that time (around Linux 3.16) and I've was busy reading stacktraces and debugging hangups for a while... Hadoop somehow also triggered some bug in transparent hugepages...
So yes, Linux is mostly plug'n'play if you need a VM for a Wordpress but IMHO digging into Linux internals can be fare more challenging than grasping FreeBSD - I guess if I had the task again I'd definitely would go with FreeBSD.
It bothers me that too much is Linux-only (or worse: Linux+x86-only) these days, making assumptions about the system that we just couldn't (and were forced to do it right) in the IRIX/Solaris/AIX days.
As someone who uses Linux, OSX, Homebrew (why, oh why?) and MacPorts daily, I can readily say we don't make our software as easily portable as we used to.