Would secutarii (or some similar category of skitarii) be realistic as Knight House infantry, if the house was bonded to the Mechanicum?
Both the Mechanicum and the Knight Houses are groups that seem to operate on a system of vows, favors and promises, rather than a standardized chain of command that you'd see elsewhere in the Imperium.
I don't think it would be particularly weird for a Knight House and a Forgeworld to have close ties, with the Forgeworld deploying a number of Skitarii troops to serve as a Knight House's infantry support, in return for a Knight House's honor-bound pledge to support that Forgeworld.
A smaller Forgeworld wouldn't necessarily have a particularly massive Titan Legion stationed there, so having the support of a nearby Knight House would make a lot of sense for them.
I'm no expert, but I think you can definitely make your idea work and (in my opinion) it should fit into the universe just fine.
EDIT: Stupid Typos...
Edited by Bishoujo, 11 May 2018 - 01:17 PM.