I think you should PM one of the community managers about this.
But my hunch is - as long as it's not monetized, it's fair use.
Although I don't know how they feel about their music being detached from their product (I mean - used somewhere else than on Elite-related video)
music is different from video material.
The main problem being public presentation, which requires to pay royalties under normal circumstances.
In todays YT culture it's not applicable any more, but that's international Mechanized Music Performance "laws" (German: Mechanische Aufführung)
In Germany the GEMA is responsible for collecting those royalties for their members (I'm not a GEMA member, for example)
In the US that would be the ASCAP. However, you'd need to contact the rights holder of the musical works, which is most likely the licensor.
I don't know the specifics of the ED OST so this is merely theoretical.
I would tend to stick to Chris' tip though. I don't think you want to get millions of viewers (but if you do, best contact the licensor)
In any case, YT will flag the content for sure, and it always depends on the rights holder how they approach such a flag.
Some block the content, others will put advertisement overlaying your video.
EDIT: The CMs probably won't be able to help you there, this is a licensing question, you best find out who is the composer of the material and then work your way through to the rights holder. (Which might not directly be Frontier, they might just own a non-exclusive transferrable license, but again, just theoretical. Don't know the specifics here)
Hope that helps.