When working with a Master Model drawing, the file that the drawing is being created is actually an Assembly and the parts, be they individual parts or assemblies themselves are Components in the 'Drawing' assembly. Basically all of the components in the assembly navigator are included in the contents of the drawing and such things as the parts list and so on.
However, we added a new option a while back to allow you to 'reference' other part files in your drawing, but in such a way that they did not disrupt things linke your parts list and so on. If you go to the Drawing module and open you drawing and look on the Srawing toolbar you will find an icon titled 'Part View'. Anyway this will allow you to select ANY file, whether it's related to the parts in the drawing file or not, to be included in one or more views. I have an example where I make a drawing of a sub-assembly and I want to include for reference purposes a view showing how that sub-assembly is used in the next level higher assembly, so I use the 'Part View' to include this 'for reference purposes only' view. However, in order to do that we actually have to add the model to the 'drawing assembly' but so that the user KNOWS which parts are part of the actual drawing and which parts were added just for reference purposes we came up with the different Assembly navigator icons. So the one with the little drawing in teh background is supposed to indicate that that 'component' is to appear ONLY on the drawing, and it does, since if you toggle the drawing display OFF, you will NOT see any of those components in the non-drawing 'assembly view'.
Note that in NX 3 and NX 4 there was a lot of confusion and misapplied views due to the fact that this icon and the one to add a normal 'Base View' to a drawing were similar and users were selecting the wrong icon, that for NX 5 we combined the two functions into a single function where the DEFAULT was adding a normal Base View of the current drawing assembly and so you would have to take an explicit ADDITIONAL step INSIDE the more commonly used function to get a so-caled 'Part View'.
Also in NX 6 we have added a filter to the Assembly Navigator so that these so-called 'Reference-Only' components can be displayed or not.
Anyway, I hope that helps.
John R. Baker, P.E.
Product 'Evangelist'
NX Design
Siemens PLM Software Inc.
Cypress, CA