pid_file = /var/run/nrpe/nrpe.pid
One fix would be to update the config file to the newer version in the 3.2.x series, but that is not going to work for a lot of people.
I have worked with Andrea Veri to work out a functional change which will allow for systemctl to work properly without needing the pid_file. This is by removing the PIDfile and making the startup a simple versus forking daemon. I have built nrpe-3.2.1-8 and it should show up in epel-testing in the next day or so.
Please, please test this and see if it works. If it really works (aka after 24 hours of an update it is still running, please add karma to it in