ok, rhevm-3.5.1-0.1.el6ev.noarch - added a host as xmlrpc, then maintenance, then change to 'json' (failed as expected: "The reason for this is that "json" isn't a valid value for "protocol", currently it must be "xml", "stomp" or "amqp".), then 'stomp' and it worked. host was activated successfully.
Since the problem described in this bug report should be resolved in a recent advisory, it has been closed with a resolution of ERRATA. For information on the advisory, and where to find the updated files, follow the link below. If the solution does not work for you, open a new bug report. https://rhn.redhat.com/errata/RHSA-2015-0888.html