I haven't played these games myself neither, so my knowledge is limited to what I saw on YT or in ads or forums.
The introduction of SoM/SoW original creations in tabletop campaigns depends - IMHO - largely how much you care for canon and Tolkien lore as the standards for the rules and boundaries of the campaign.
If they are not a priority (and Tolkien's Middle-earth is used more as a suggestion or inspiration) then this stuff is likely very useful and enriching for the campaign. OTOH, if canon/Tolkien lore is important, these things might be used as something that people in the game world might believe in (as existent) when they are actually not (i.e. an false in-game belief/information). As far as Tolkien lore is concerned, these things might best be described as "partially inspired by motives from Tolkien's Middle-earth"
That being said, IMO one could use them at face value (i.e. as they were presented in these games) for a campaign if you want to use them at all, since one shouldn't be concerned about canon or Tolkien lore at this point anymore