Product and version: FileMaker Server 15.0.1
OS and version: Mac OS X 10.11.5
Browser and version (N/A)
Hardware: Mac Pro late 2013
Machine had been running OS X 10.10.5 and FileMaker Server 14.0.2. De-installed FileMaker Server 14, installed OS X 10.11.5 El Capitan, then installed FileMaker Server 15.
After the installation there were unexpected folders in the FileMaker Server folder including:
All of the folders were owned by user "fmserver" with Read/Write permissions and No Access for "everyone". It appears that instead of creating the fmserver system account with no user home folder the FileMaker Server installer tried to build a normal user account with a home folder of /Library/FileMaker Server
How to replicate
Install FileMaker Server 15 on El Capitan 10.11.5
Can probably remove the folders without hurting anything but haven't tried
Installation on OS X 10.10.5 Yosemite after de-installing FMS 14 did not produce the additional folders, it only appears to happen on OS X 10.11 El Capitan.