Segersgia wrote: I recall them being failed Aspirants for the Chapter turned servitor.
Cenobyte servitors - standard issue templar wargear since 4th edition.
They are the failed neophytes turned servitors who get assigned to the chapels of the crusade fleets and are tasked with carrying around the chapters relics, swinging insense burners, chanting, and so on. Grimaldus has always had three of them dragging around bits of the Helsreach Temple for instance.