Only brahmanas can serve the deities.  So, when a temple requires brahmana devotees to serve in their temple for the deities and cooking, selects a few hari nam initiated candidates who are REALLY qualified.

If anyone is working somewhere, he is a sudra. Srila Prabhupada asks why a sudra should become a brahmana as he can get the same status attained by a brahmana if he serves the lord as sudra itself.

One thing is clear: Hari nam initiation itself is enough to go back to Krishna if you follow the diksha rules properly (Mainly, chanting and following regulative principles).

Those who are working somewhere or those who are not going to do deity services or cooking services need not take Brahmana diksha.