[@The Fated Fallen] No it isn't odd for the mechanicus to have some level of presence on a hive world, given the nature of heavy industrialization & infanstructure. Some agents would need to be on-world to make sure everything doesn't fall apart. As far as storing artifacts, again not really I suppose. If they discovered something and felt it was safer or easier to keep in on the surface rather than remove it to a forgeworld. Or they could better disguise their facility & research from prying eyes by keeping it on a civilian world. It's happened many times before in the lore, and in those instances a detachment of skitarii guardians would not be out of question. 

I was just curious as to the angle you were playing. It wasn't meant as a hard critique of your choice.