That is nothing new, in fact his entire system is repackaged from Tempel ov Blood who's leadership admitted to have originally created it as exactly that: An occult MLM scheme siphoning energy from the "unworthy voluntary opfers" into the "blood pool". May sound too social-darwinist of me, but I approve of that, people know what they're getting into, and most of the time they are attracted by the empty promises of being empowered to harm other people, so I guess they are going to fuck around and find out, and some wouldn't survive the "find out" phase. These "vampires" are similar to people who set up pedophiles trying to meet up with children, just to rob and abuse them, it may be true that most of the time people doing that aren't moral beacons themselves, but it's not like the "victim" can call the police on them, as even the victim knows that they got themselves in this situation by attempting to hurt others. Ad Gaia, qui laetificat juventutem meam!
I would like to learn here. Tell me what historical sources are there for Noctulius?
For the entity Blackwood claims to be affiliated with? ONA MSS, as well as a few internet articles by it's initiates, there's nothing else, as Noctulius originated in the ONA and his further reinterpretation as a god of vampirism originated in it's American offshoots. I'd also point out that ONA's original MSS are intentionally vague when it comes to describing the Dark Gods, encouraging the reader to contact these entities themselves to "Fuck around and find out", so if you want something concrete, look into materials by Hagur, Ryan Anschauung, V. K. Jehannum, Draugr Coven of Azanigin or basically anything that is related to the ONA but isn't exactly a part of AL's corpus of works.
BTW you sure he is celtic? He is not in the Wiki list of celtic deities.
It's been a while but I only ever remember him being mentioned as a Celtic deity once, in some old dictionary of Latin terms, with no footnotes or links or anything similar, and these old dictionaries are at times full of random nonsense.
It's not entirely impossible, there are many minor deities that are only mentioned once and known by their titles in foreign languages, Scythian Ares and Celtic Cernunnos are the most well known victims of that phenomenon, the later, by the way, being heavily associated with the ONA's Noctulius, perchaps there was in fact a deity of Celtic origin known to the Romans as Noctulius and mentioned once, in passing, in some document I won't bother looking for, but there definitely isn't a connection between him and what modern wannabe dracular attempt to invoke, though these people do tend to obsess with obscure celtic gods, a courtesy of Ryan Fleming, a certified British patriot and a serial child molester. The name itself may also be entirely invented, when coming up with a name for an ancient god it's very easy to just say "yeah this evil cult worships the uhmmm... Night... guy... yeah Night guy of the night, and they only worship him at night because he is the Night guy"
However, a certain
fellow connected the name Noctulius to Nyktelios, an epithet of Dionysus, associated with secretive initiatic rituals, which is perfectly in like with ONA's Noctulius, and sounds entirely realistic to me, knowing of DM's interests in Greek mystery schools, besides there already existing a direct parallel: Another ONA god Sauroctonos is also named after an epithet of a Greek god, this time Apollo's. I understand Noctulius as a name for Dionysus, and I dont recall him ever denying that or correcting me.
I also very clearly remember there being a wine brand Nyktelios, not sure if it's any good, but perchaps instead of trying to drain their neighbors of energy, Mr. Blackwood should drain a bottle of Nyktelios of it's contents once in a while.