If that is true, then what role do Counts and Viscounts play INYTU?
Counts, Viscounts, and Barons of various worlds form the subsector moot, serve on the subsector committees, and fill subsector ministries, as well as providing local appellate to imperial official and imperial oversight of local government.
Some terms:
Fief — lands ruled by a noble
See — Lands which the Noble is acclaimed of, but which are not rule
Breaking this down...
Each Subsector fief is a ducal or county demesne (his personal fief) plus a see of the whole subsector, plus heading the subsector goverment.
The subsector canonically has a moot comprised of the nobles of the subsector
The subsector canonically has high courts. (Appeals are made to the local nobles, who may pass them on to the high courts. High crimes are charged directly through the local noble.) To be an officer of said court, one must have at least a knighthood (canonical).
The subsector has some oversight over local ministries. Dual authority, just like the Navy.
The Subsector Government has the numbered reserve fleet. It answers directly to the subsector noble, and he probably appoints secretaries over Naval and Marine components, as well as an intelligence secretary. (5FW boardgame library data implies.) There are likely also Secretaries of Trade, Calendar Compliance, Colonization, Justice, and Communications. Each has probably small bureaucracy.
The Subsector Moot canonically makes the laws for the subsector, with the voice of the Duke being essential to passage.
Canonically, some subsectors are ruled by counts, instead.
A few subsectors are subject to other subsectors; they are fully part of the other subsector's moot and government.
On their see world, the world nobles have pretty much free reign to investigate, and serve notice on behalf of the subsector government, violations of imperial law and sector or subsector policies and laws. They cannot impose sentence; they present their findings to the moot or the courts. It's up to the local world whether their investigations may also be served to local courts for local violations; if nothing else, local prosecutors and police generally will take into advisement anything the Noble has investigated for further scruitiny.
Local nobles may raise Huscarles - troops trained locally, but equipped to whatever standard the Noble can afford, often to IM or IA standards, seldom more than a light regiment. (Norris' Huscarles are the second largest such unit in the 3I... at a reinforced regiment.) These platoon to Battalion level units usually are spit-n-polish affairs for active duty troops seconded. Some are crack fighting units comprised of high skill troopers. If nothing else, the troops tend to be senior - line troops are E3, and NCO slots are up one grade from expected, if not two. You might even see a Platoon lead by a Captain with a Sergeant Major as his PltSgt... and every trooper a 2-term corporal or buck sergeant. Huscarles vary wildly in strength and organization.
IMTU, the Count of Regni, on Regina/Regina, has a "regiment" of huscarles... It's organized with short squads {5 man}, 3 squad platoons {17 men 1 officer}, 2 platoon companies {36 men, 5 officer}, 2 company battalions {75 men, 15 officer} and the regiment is 3 battalions {230 men, 50 officer}. It really is a small Battalion in numbers... but it's all TL-15 IM grav-belted Battledress equipped infantry, alternating between security at Regni Downport and the County Palace. In a pinch, they can be trebled with IA troops to make a proper light regiment. They're officially a Military Police Regiment...
Further, the various fief-hexes can be important elements.
IMTU, they're usually the downports.
IMTU, Regni Downport is the fief demesne of the Count of Regni.
The High Port is one of the hexes of the Duke of Regina's fief. As are the two other imperial downports. And one of the other moons of Assinoboia, in total.
Likewise, the starports of Terra. AECO is the planetary Count, Phoenix is the Viscount of Phoenix, Adak is the Baron Adak's, and Baikonur is the Baron Baikonur's. Guyana, China, and Wester Australia are knightly port-fiefs.