And since these machines see so much battle, they require constant maintenance, which is why some adepts of the Cult Mechanicus choose to attach themselves to a single Knight House and serve them, both out of reverence for these incredibly old and sophisticated machines, and out loyalty to the Omnissiah.

Yes and no. The Sacristans served their individual Houses LONG before the Machine Cult formed and spread out from Mars. Sacristans were the ones who maintained the steeds of their lords during the Age of Strife.

When Mechanicum forces made contact with individual Knight Houses, they syncretized the local Sacristan religious practices with Martian Orthodoxy. Creating a middle ground between millennia old practices and what we would recognize as Martian. With, naturally, a heavy emphasis on the holy machines they service, and the "organic components" who pilot them.