I've mostly been so against this incarnation of the Borg. Everything we've seen in the Star Trek universe regarding the Borg is centered around their first encounter with the Federation via a "Q" introduction with the USS Enterprise NCC-1701D in TNG. Based on the timeline, the Borg didn't know about the Federation until "Q" made the introduction "ahead of schedule".
So, seeing them in "Enterprise" just doesn't make any sense... at least so I thought, until I watched the episode again. And then, I kind of changed my mind. Here's why:
1) We never hear the word "Borg". Thus, whatever record of these beings is made, it is not tagged with that eye popping label.
2) Flox mentions the "collective" experience, but perhaps he doesn't add it to the ship's log.
3) The Borg that were encountered were certainly weaker than the version we see in the TNG and beyond. Perhaps at this point, the Borg are at a lesser point of technological progression. Certainly we see the nano probes affecting the people at a much slower rate. And the antibodies in Flox confused them enough to let him slow their progression and eventually eradicate his body of the nano-probes. Unfortunately, the technique would be unsuitable to use on human beings.
4) How'd they manage to get to Earth in the first place? "Star Trek: First Contact"... Borg ship remnants that managed to survive reentry and crash in a frozen wasteland. Despite the Borg locator signal sent prior to their destruction, it's possible that the Borg busied themselves with other species before concerning themselves with the long distance target of Earth. Or, perhaps the message dissipated before it could reach any other Borg within range.
So... I think there's enough to go on that can sidestep a major timeline violation. It was an entertaining episode. But, because it's an isolated incident with no contribution to the rest of the Enterprise series, why did they bother? Well, perhaps convenience. They've got all the Borg costumes and alcoves, so why not leverage it?
