I was just looking into this to see if I could help, having lived in Korea; last time, taught design in a then-new graduate school, KAIS, which was a while ago. Though I’ve forgotten most of my Korean, I can still work with the text.
First answer is to Starlight. Ioa/Amber, maybe you could email him, as he looks to not be in touch, and I know you have the ability for that from previous work we’ve done.
Starlight, I’ve been able to get your situation to work. You can find a picture below. The way I did so, in the end, was to discover an English-named download of the extra fonts you want, Nanum.
You can get the whole set, including Extra Bold, here, as Windows OTF fonts: Nanum OTF Set
As you’ll know and I could figure out, the main site says the font is free to use for anyone. The page I found the Windows OTF font on is hangeul.naver.com/font.
When you install these fonts, then open Scrivener (or any other text program) you’ll find the fonts under NanumGothicOTF, rather than the Korean/Hangul name. I found Scrivener to handle Regular, Bold, and Extra Bold reasonably well. The Extra Bold will appear as its own NanumGothic fontname in Scrivener.
If you set text in it, any of the Nanum variants will save properly now, and also Compile or Print. If you compile to RTF, Word will successfully show the Nanum font variants, and will print them correctly.
The RTF doesn’t work quite so well for InDesign import (Place), but the text will be there, and you can quickly correct the font types by creating a style and applying it to all your titles, for example.
I also found a little difficulty with the Nanum font as far as how it’s handled in Scrivener compile to PDF: the text isn’t selectable in the PDF. However, if you print from Scrivener to Acrobat, then the PDF comes out ok.
This should give you a practical situation, Starlight, keeping in mind that Scrivener is a writing program, and not a page layout system like Word or InDesign.

Now, what do I have for the team, and before I fall asleep here Thanksgiving eve?
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indeed, MimeticMouton appears to be on the right track, that full or partial utf-8 font names aren’t handled well.
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There are a number of furry, funny things in what comes out the compiled RTF for this particular utf-8 font, anyway. The RTF is successfully eaten by Word, but not by InDesign. What’s more, though Word can print well from the RTF at least on simple examples, it can’t save itself in RTF, DOC, DOCX etc. with any better results. Symptoms include mis-labelling of the font targets: Regular, Bold, Extra Bold are not properly assigned. Easy to troubleshoot with the free release of this font, link as above. I didn’t have better results trying export as DOC.
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one more interesting thing that turned up was a non or pseudo-font, which Scrivener probably doesn’t want to show as it’s not intended for use. Here’s what Adobe has to say about it; the Dov fellow is a prominent person there.
http://forums.adobe.com/message/3996613
You see the mangled fontname, if this font exists on your machine. It looks like ‘dobe’, at the end of the font list when you are choosing a font. If you choose it, the display on the unopened menu is the actual name: ZWAdobeF. I’d suggest making sure the font choice dialog(s) don’t offer that font.
Regards,
Clive
Edited to put in the Adobe link – really was half asleep last night! Happy Thanksgiving, all.