The original Japanese text about vampire incident is vague enough to allow for various fanon interpretations in Japan. For example, there's a fanon where Remilia was the only one who signed the contract, and by its demand she killed off all other invading vampires.
I've carefully pored through all the related parts in PMiSS before, and one thing still bugs me: it says the SDM became notorious after the scarlet mist incident, suggesting it was unknown before. This can be construed as a very strong hint for Remilia being not involved in vampire incident. Of course it's easy to come up with several ways around that. I prefer to think SDM was only moved into Gensokyo after vampire incident.
It's stated that the SDM was unknown by "humans". At least, in the translation at the endings wiki (er, or whereever it's stated). One of Aya's news articles in BAiJR, however, has the prism river sisters hold a concert at the SDM, and the article is dated several years BEFORE EoSD, which pretty much proves that youkai knew about the SDM (and that the SDM existed) quite a bit before EoSD.
PMiSS never specifically directly says that Vampire is Remilia. However, it does say in Remilia's section, "When one refers to vampire in Gensokyo, they must be talking about the Scarlet Sisters." It'd be pretty stupid of Akyuu to say "When one says Vampire, one means Remilia" in one section, and then say "Vampire" without meaning Remilia in another section. IMHO that's explicit enough, but no, it's not directly stating or confirming (in some interpretations) it, technically.
Some people might argue that if Akyuu really did mean Remilia for the Vampire Incident, she would have mentioned Remilia's name at least once in that article. However, apparently not mentioning Remilia by name is accepted Gensokyo culture. Even Sakyua's section in PMiSS only refers to Remilia as "the vampire". And in the entire rest of the Touhou series, no one ever refers to Remilia by name either, always referring to her as "the vampire" in most cases, and "mistress" in the case of SDM residents. The only times people have ever referred to Remilia as "Remilia" instead of "the vampire" or "mistress" come from official sources before PMiSS (far as I can tell. Yes, I did pay a lot of attention to whether or not anyone called Remilia "Remilia" in anything, and... no one ever does, after PMiSS. Except maybe Patchy but she wouldn't call Remilia "Mistress" or "The Vampire" for obvious reasons). For whatever reason, with PMiSS, ZUN decided that it'd be an in-story cultural thing for everyone to never refer to Remilia by name, so in that regards, Akyuu not bothering to refer to Remilia by name in the Vampire Incident description makes sense.
As an aside, the Japanese wiki doesn't have text-by-text transcriptions of official works like the English wiki does (from what I can tell). So I tend to personally take Japanese fandom with a grain of salt when trying to see if it implies what's canon and what's not. Still, it is true that PMiSS never explicitly states that the vampire is Remilia. In my opinion, saying "When one refers to vampires in Gensokyo, one must be referring to the scarlet sisters" is pretty much just one inch short of directly naming Remilia anyways, but others' mileage may differ. Hilariously enough, I woudln't be surprised if the English fandom had a better grasp of both Touhou canon and "what's likely Touhou canon that ZUN doesn't explicitly say because he stated he keeps some facts to himself or close friends" due to this. Most Japanese wouldn't have access to the direct text that does things like show no one calls Remilia "Remilia" or the date of that BAiJR article (though they might be able to put two and two together if that Japanese timeline had the article in it. That'd take quite a bit of sleuth work, though).
As an aside, someone did finally get around to making a doujinshi of te vampire incident with Remilia as the vampire, showing that at least some Japanese fans feel that she is (of course, the youkai that seems set to stop her is Yukari). The thing wasn't completed though..... I think.