You could import it, and maybe work out how to use it, but I wouldn't recommend it. Between a lack of double buffering and that it's not optimized for game code could leave you with flickering and laggy graphics. I am also unsure how well that would port to Xbox if you were to do so.
and additionally I think you can now have XNA active in a WPF project, but that's a bit more complicated than I understand... Maybe someone with more experience can pitch in on which of these they would recommend, or another one I didn't list perhaps.
Aha! Found it. So apparently some OpenType Font setups will not work. It's a misleading error message. To quote an exerpt from where I found my answer:
The OpenType requirement is a bit misleading as the font has to have TrueType outlines; OpenType also supports PostScript outlines which do not work in GDI+, which is what the SpriteFont processor internally uses.
So I did an online conversion from otf to ttf and reinstalled my fonts with the TTF files, once I restarted visual studio again after that, it worked.
It's an open type font, but the error specifically states that it has to be open type or true type, so it's covered there. I am mostly attempting to use the name "Trajan Pro" with any variation I can think of. The 'friendly name' as far as I can tell is Trajan Pro according to the font folder and notepad/wordpad/word, etc. Which all show Trajan Pro as an option and work. Hmm... is there any way to load the font directly from the file, say if I include it in the project directory?
If you load the file once in the load process and save it into an object stored in memory it won't have to reach out to the filesystem to read the data every time. It's expensive to read the file each time, so if you store in the load, the draw process won't have to read the file to get the information.