You know, it’s totally plausible that Sweepers could be Bloodfiends or at least have some connection to them.
There’s proof by the end of Intervallo 7.5-2 teases, there seem to be a lot of similarities between Bloodfiends and Sweepers, especially in their hierarchial structure and the thirst for "fuel". It is particularly interesting that Sweepers inflict bleed and empower themselves when the status effect is in play, which is how Bloodfiends function as well. I might be reading too much between the lines here, but there is also another subtle hint. Don Quixote annoucer has a special line that triggers when she fights against Bloodfiend or Bloodbag enemies (at least it never seems to have triggered on other enemies).
This line is also present in the final fight against the Sweepers. This could be an oversight, but given the tease, I think it could foreshadow the Sweepers' true identity.