Well as stated above I accept I am on shakey ground, however, let me present an argument if only for the sake of continuing a fruitful debate (I hope you see it as such tooThat would be, "Member Worlds cannot be interefered with by the Imperium." Which is found all over canon.

As stated above the essence of true feudalism (as opposed to bastard feudal or later honour nobility systems) is the contract where an estate in land is granted by a lord to his vassal on condition of rendering homage and service.
The American Heritage dictionary describes feudalism thus:
'A political and economic system . . . based on the holding of all land in fief or fee and the resulting relation of lord to vassal and characterized by homage, legal and military service of tenants, and forfeiture.'
Therefore the feudal system works because Emperor grants land to Duke who grants land to Knight who grants land to Peasant who farms it. In peace the peasant pays rent for the use of land, in war the peasant provides military service to the Knight (i.e. the peasants form the infantry). The Knight provides military service to the Duke holding the land and so up to the Emperor.
Lets look at Library Data N-Z as an Ur text of canon:
'All nobility is part of the feudal system of Imperial government' p.34, para.5
So the Imperium is feudal (to some degree) - therefore the fief for service paragigm must be in place to some degree or there is no sense in calling the Imperial structure feudal.
To continue:
'The Emperor is the ultimate object of thousands of oaths of loyalty and fealty. . .' (p.36 about para.8)
So the Emperor is offered fealty - i.e. he gets something in return for making people nobles and that is service. I would argue that in a feudal context this is specifically military service in one form or another (eg. tax or men).
and on:
'Patents of nobility...may include fiefs of land. . . The fief is a convenient method for the Emperor to reward certain nobles.' Libr.D. N-Z p.36
OK - first contradiction with real feudalism - land is give as a convenient reward. BUT land is given, and that land is not part of a world government's possession, it is land belonging to to the noble by reason of his title (reference is made to a Knight holding either a large plot in the wilds or a singe hectare in a business district).
Mix that with feudalism and we have a situation where the Emperor can call in the favour - in true feudalism this is either money or arms.
Imagine this: A traveller Count might have fiefs on each of his three or four worlds. As a count he may have very large fiefs indeed. He is not interfering with a world government as the Emperor has given that land to the Count as his personal and heritable property in return for service.
The Count has a choice - he can rent out that land to individuals, companies or even the world government who develop it for profit; or he can leave as his personal hunting ground and exclude all from it. Assume he lets it out. As this is feudalism, the rent may be money tax in times of peace or men tax in times of war. In any event the Count is charged with providing fealty to the Emperor when called upon, so I would expect the Count to make sure that he can do so in such an event.
Remember canon says that the Imperium is feudal and a fief is personal. If it was a continent one would expect at least a money price as rent. If it was truly feudal the Lord could demand conscripts from among those vassals who have the benefit of his lands.
Unfortunately canon doesn't really say how big a Count or a Duke's fief would be.
In my view, therefore, it is possible to argue from canon that a high noble had a right of conscription from his own lands without interfering with world governments.
I might, of course, be entirely wrong.....
