Just to be clear - facts are statements of nigh-indisputable truth. I am not sure that applies here. Mostly people say fact when what they really mean is collective opinion on a topic. Neither I would say apply here, to be honest.
And while I agree it is most likely the White God that Nicodemus is referring to, it isn't fact YET. That would require some exposition like Nicodemus saying to Dresden "The Enemy I fight against is The Almighty himself" or something along those lines, or Jim saying in an interview that the Enemy that Nic was referring to was TWG. But we don't have either of those. We just have speculation - which is deliberate on Jim's part (otherwise he wouldn't have used the label "The Enemy" and just said whoever Nic's great enemy is).
He could mean Lucifer, or an Outsider/Old One, or some other being we don't know of. The point is, the identity of Nic's "Enemy" is up for debate still and will be until we get further evidence.
I will give you that he could be referring to Lucifer. I should clarify... when I said fact it was with two stipulations. First that the options were Fact or Opinion. Within that dichotomy it is more accurate to say Fact. Second the fact is that Enemy isn't a reference to Nemesis rather than that enemy is a reference to TWG.
If the discussion were about Enemy meaning Lucifer or TWG I wouldn't have claimed it was a fact.
If the question wasn't asked (Fact or Opinion) I wouldn't have claimed it was a fact.
I probably shouldn't have claimed it was a fact, or at least not claimed it as hard as I did. I should have said it was more a fact than an opinion.
Enemy isn't a name for Nemesis. Adversary is. And that line can't be read as a reference to Nemesis even if Enemy was a name of Nemesis because the coin isn't left, the fallen isn't left, and dead mortals don't fear Nemesis...
I find it unlikely that Enemy refers to Lucifer, I find it impossible that it refers to nemesis.