They certainly are Realms canon. All the early and mid-period Realms Dragon articles are presented through the framing device of a person from Faerûn, usually Elminster, coming to Earth through gates and speaking to Ed Greenwood (or Jeff Grubb or Steven Schend), and all Realmslore implicitly comes to us through such unreliable narration. There are scores of such world-links in the lore, in fact they're the basic premise of the "Forgotten Realms": many connections between worlds, but those to our Earth have waned.