Actually I've never seen the animated series and I don't think I've read the story, though it's possible.
Oh, if you'd read FTGG, you'd remember...
What happened was that I described the hotel before I realised that Lex was going to be there [...] Once I'd realised that Lex was a logical choice to be the vampire, I knew that there would have to be kryptonite.
Well, you see, that's the thing: just because Luthor is there does
not mean that there
has to be Kryptonite, and it's a shame that so many people make this assumption. I would go so far as to say that even your story suffers for that automatic correlation: if VampLex has the K, why does he need Willow? He
knows what Kryptonite does to Superman, so all he has to do is arrange an ambush, just as he did in S1, and then he only has a powerless Clark to deal with; and he'd
love that! It's classic post-Crisis/L&C Luthor -- taunting a powerless foe, especially when said enemy is now much weaker and slower than his enhanced vampiric level instead of the other way around, which means that he can have the fun of beating him up and killing him personally, perhaps finishing the job by drinking from him.
Not only that, but a good argument can be made that VampLex shouldn't even be able to
get any Kryptonite -- not in the L&C continuity. The only known pieces are those from Schuster's Field, and all that's left of that (most of it having been destroyed) is at STAR Labs (or is that fanon? Either way, the show had K as a very scarce commodity, to its benefit). If Luthor had to have a weapon, it would fit better if he'd had another quantum disruptor or disbander; again, he knows that they're effective against Superman, and he knows where they're stored or where to get the plans.
Another late edit - Back when I was ten or so and reading Superman comics in the early sixties I recall him having some Kryptonite-proof clothing he used in the laboratory in the Fortress of Solitude. I'd forgotten it when I wrote this chapter and wrote my earlier reply, but it was probably in the back of my mind.
Oh, there's a long history of that in Superman media of all types; I remember an episode of the 1960s Superman cartoons in which he hid in a section of lead piping and then used it as impromptu armour against a Green K zap gun. Lead glass, lead-based paint -- you name it and it's been used over the years. Personally, my favourite twist that way is having Green K as the active ingredient in the drug that protects Daxamites from their hyper-sensitivity to lead
Phil