Any reader may very reasonably retort that giants and elves are unacceptable even in earlier centuries of the Technic History timeline. Such literary sensibility is to be respected. In that case, fantasy and hard sf story lines still coexist but in the Old Phoenix multiverse, not in a single universe.
The issue of continuity between diverse series arises in two contexts. Either a single author writes many works or a single publisher links works by many authors. ERB linked all his series. Michael Moorcock has a Multiverse, as does Poul Anderson even if that terminology is not used.
I quote Alan Moore on this subject first because Moore's writing is beautiful and secondly because it is relevant to how we might envisage relating Anderson's many series to each other:
"...all the comic book stories produced by any given publisher are likely to take place in the same imaginary universe...Try to imagine Dr. Frankenstein kidnapping one of the protagonists of Little Women for his medical experiments, only to find himself subject to the scrutiny of a team-up between Sherlock Holmes and Hercule Poirot...
"Imagine for a moment a universe jewelled with alien races ranging from the transcendentally divine to the loathsomely Lovecraftian. Imagine a cosmos where the ancient gods still exist somewhere and where whole dimensions are populated by anthropomorphic funny animals. Where Heaven and Hell are demonstrably real and even accessible, and where angels and demons alike seem to walk the earth with impunity."
-Alan Moore, Saga Of The Swamp Thing (New York, 1987), p. vii.
Yes. Anderson has Sherlock Holmes, some universes full of alien races, others not, ancient gods, Heaven, Hell and demons. If there were to be any more Anderson multiverse stories, then Alan Moore might be a good choice to write some.