The Skitarii are the warriors of the Adeptus Mechanicus. They generally have more advanced weaponry and equipment than their Imperial Guard equivalents, due to the technological expertise of their Techpriest masters.
Codex Grey Knights page 51 with a Coteaz army. So yes, you must take Coteaz in order to make inquisitorial henchmen a troop unit, but check this out.....
Some Inquisitors induct only fromthe gloried institutions of the adeptus Terra: the Schola Progenium, the Skitarii Legions or the Chambers Militant of the Ecclesiarchy.
So yes, you can take Skitarii in your forces. With some customization you can make an entire skitarii force. Look at some of the different skitarii types that exist.
Hyspasists: These are the basic tech-guard infantry, and are armed with lasguns. They are more augmented than the normal Imperial Guardsman, and may have received emotional-suppression surgery.
Praetorians: These are the elite of the Skitarii. They are super-enhanced (bionically/cybernetically/chemically/genetically etc) humans who are augmented with a huge array of cybernetics and heavy weapons. They are, essentially, a sort of counterpart to Obliterators.
So what I am suggesting, and am planning on building is a Coteaz force, with skitarri Hyspasists as warrior acolytes, and praetorians with jokaero weaponsmiths. Throw in some dreadnought walkers, some techmarines, and you have an army.