Huscarles have special status. They are a noble's personal household troops and are limited in numbers according to the Emperor's whim (alongside his patent of nobility a noble receives a document giving him the right to raise so-and-so many huscarles). They also have special priviledges when acting on behalf of their noble. And they are permitted to every high noble down to barons, whereas only high dukes have interstellar governmental authority (Though presumably a duke can delegate his authority to lesser nobles). Ordinary duchy troops would not be huscarles.Somewhere, (GT:Nobles?) it says that Huscalers are "consider part of the Unified Armies of the Imperium, even though they are commanded and maintained by individual nobles.
It's ducal and planetary. Both are colonial, i.e. raised and maintained locally.It seems logical to me that if Huscarles are considered part of the imperial combined armies, they would be trained, regulated and equipped in the same manner as regular troops. It also makes sense that Ducal and colonial navies would be organized along Imperial Naval lines to improve integrations in times of crisis.
It's certainly practical to train your armies and navies to Imperial standard, and no doubt many dukes and a fair number of member worlds do just that. But to allow for customizing duchies, I think it should be possible that dukes can organize their units any way they find best suited for their particular duchy. The whole point of splitting the Imperium up in fairly autonomous units is to allow for local input in organizing local affairs.
It's nice to be able to introduce the odd quirk. Someone once told me that the Danish navy, being quite small, used liutenant commanders to captain its MTBs whereas the Americans and the Brits used mere lieutenants (or some similar discrepancy). The result was that in joint operations, the Danes tended to wind up in charge of combined MTB units, no doubt to the chagrin of a number of American and British lieutenants. I haven't used that particular quirk yet, but I could see how that could be a way to distinguish a small duchy somewhere.
Another example: Vilani colonial forces probably organize their militaries and navies in the traditional Vilani way, whatever that may be.
Hans