Leopardus wrote:
There seems to be consensus amongst posters on the various forums (optimism perhaps?), that it is the case. Server 5 can be used to manage a Yosemite and El Capitan. We have also seen an update since (not altogether strange), but before server was bound to a specific iteration only. Some authors seems to agree on this point, if you read their books.
OS X Server version 5 is compatible with OS X 10.10.5 and later, per the compatibility section at the left of the App Store product specs.
AFAIK, this is the first version that does have that compatibility, however. OS X Server 10.6 and earlier — which had separate distributions, and cost US$500 and US$1000 for the 10-user and unlimited-user packages, respectively — and the Server.app tool that is an add-on purchase for 10.7 through 10.11 have also been version-specific. Though not with this most recent Server.app 5 version, as mentioned in the Apple specs.