To a large extent (there are a very few exceptions) the NX API does not care what module it is in.
To work in "drafting" just open/display a drawing sheet.
Note for the example of a surface finish, (before I assume) have you already tried using the Siemens supplied surface finish symbol?
I would also investigate using a custom symbol for this.
(Upgrades are easier the less API code you have to deal with)
But if you do use a UDO, one suggestion I would have is to add an integer parameter for "version" (i.e. the version of the UDO itself). Because you'll release your code to production users, then someone will need an additional parameter (or 5 or 10), so you add it, but now your code will have to handle old UDO instances (without the extra data) as well as new ones (with the data). For your program logic, it is typically easier to just check the "version" parameter to handle the different cases, or upgrade "old" UDOs to the latest "version".
Production: NX10.0.3.5 MP16/TC11.2
I'd rather be e-steamed than e-diseaseled
To select objects in a drafting view (such as a drafting line), you'll need to use the .SetCursorView method. I think it defaults to the work view, which is the drawing sheet. Using .SetCursorView(0) will allow selection within any view (drafting view or sheet).