This is most likely because slurmd and other Slurm programs are looking up _slurmctld*.*_tcp without appending a domain name.
The default behavior of the Linux resolver is to treat lookups contains one "." as a FQDN and therefore no domain search is done and the query will fail.
To get around the problem add "options ndots:2" to your /etc/resolv.conf file or even better if you build your own copy of Slurm go to the src/common folder and locate the file slurm_resolv.c where you add res.ndots=2; after the call to res_ninit() and before the call to res_nsearch().
Compile and you will have a perfectly working configless configuration.
You may want to vote this SchedMd BUG report to get the solution into the official distribution.