There is a necron personality trait (if you can call it that) which is they are obsessed with human technology. So it'd be like how modern humans are obsessed with medieval.
There is an ad mech branch based solely on the study of xenos technology. Idk why though but they still are loyal to Mars.
So to sum it up. They Don't need to be heretics, and it be a "I scratch your back, you scratch mine" relationship. (I imagine a tech priest and a necron noble meeting behind a dark alley but instead of a drug deal its a tech trade).
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