For the movies:
He just simply made a Side Bet on whether or not Seth would survive the night.
And not like "oh, he suspects", he knew. Notice that Seth always says stuff like "That guy didn't recognize shit" whenever Richie tries to explain why he did things. This would also explain why Seth acts much calmer than one usually would be if they encountered something Richie did.
If you pay attention to their behavior before the attacks start, they're not really paying attention to the dancers. Frost is focused on trying to build a tower out of dominoes, and SM seems to be testing various people to see just how tough they are. They also seem totally unfazed when the staff start changing. They just stand up and get right to the monster-killing. They were probably vampire hunters who came to the Titty Twister to do their thing.
For the series:
Ranger Gonzalez's very existence is the single biggest difference between the movie and the show. His presence at the Titty Twister will result in the big fight playing differently than it did in the movie, resulting in Santanico's survival.
Seth from the movie is his idealised version of himself, The Ace who runs the whole Gecko operation and always gets what he wants. Ritchie is turned into The Load who Seth spends the entire time cleaning up after, and any indications of his actual skills are carefully removed. Santanico, depsite being a driving force behind the entire story, is reduced to a bit part and is quickly dispatched by Seth after a Bond One-Liner. Carlos is turned into a clueless idiot and Ranger Gonzales is removed entirely, as it sound better if they eluded the entire police force and got into Mexico with no help. Kate and Jacob, are still portrayed positively as they're the two Seth actually liked.
The second half of The Movie is basically a macho gorefest that serves to make Seth look like the ultimate badass, with the Mercy Kill of Ritchie added to make him sympathetic. His experience with the labyrinth, a dark meander through his troubled past that he wouldn't want to be sharing, is replaced by a final stand-off with the vampires, which he ultimately wins. Even the ending gets changed to his benefit, he gets the money, the life in El Ray, and a Pet the Dog moment with Kate. Instead of the reality of losing everything and hitting rock bottom.
- That one technically isn't entirely possible considering the series is a parrallel universe reimaginging of the movie to begin with. Then again, could be wrong there. Besides Word of God says it's in a parallel universe anyway.
Howard lived in Texas, the culebras' back yard and his stories have an overabundance of evil snakes, dark cults and serpent men who masquerade as regular human beings. This interaction may also be where Lord Oculto got his interest in pulp fantasy from.
Specifically from the Tlacique bloodline. They show all the telltale signs, from displaying snake powers, emotionally manipulating their victims and even being capable of disguising themselves as others. They worship ancient Mexican gods, and perhaps their relationship with the spirits of the land have made them more resilient than regular vampires, even allowing them to walk in the sun for limited periods, something regular Setites would find especially abhorrent.