No, it's a good question! Including a single identifier for the specific adaptation within the character/relationship tag should do the trick, because then that tag shouldn't be confused with the same character/relationship in a different fandom. So, for example, you could nominate the Good Omens (Radio) fandom tag, and within it the tag:

Group: Aziraphale/Crowley (Good Omens Radio)

And then it won't be confused with either the novel or the miniseries.

Let us know if you have trouble coming up with specific clarifications for any of your nominations!