Yes, it is entirely possible that first the Clinton machine & Fusion GPS hired Shearer for standard opposition research, then they needed to up the ante (by enlisting the FBI on their side) so they got Steele to effectively republish the opposition research under his own name, thereby wrapping the baseless conjecture in an aura of “intelligence” from a “former MI6 agent”.
Maybe, just maybe, the first FISA application was based on the Shearer memo, and when it was denied they drafted Steele to polish it up before representing it, maybe to the same judge or maybe to a different judge.
Certainly possible.