@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.
Not for me to say, GM's call. He looks cool. my only question might be, what is a skitarii doing on-world, were they guarding a cult mechanicus facility or...?
Not necessarily. If no one wants to play one they can always be NPC'd and doing their thing in the background. You can even make it a point of the game. Someone onboard is killing tech-adepts! they have to be found and stopped or else shit will go sideways real quick.