Hello,
I think there are a few rules missing into the drbd-selinux package as standard behaviour that should be allowed, isn't.
I opened a bug into RHEL bug tracker but either I queued it up on the wrong queue (I didn't know if it's for the drbd folks, or the SELinux guys...) or nobody is looking at it. Here it is: https://bugzilla.redhat.com/show_bug.cgi?id=2456191
Ciao,
Luca