I would argue that Horror can work in Star Wars, due to the fact that it isnt anything new to add horror to sci-fi, and star wars isnt a stranger to using horror either. The Clone Wars had that battle of Geonosis and the Brain Worms. Like that crap was scary man. But thats not all either. You also had Mauls faith in the Clone Wars (before he's found), that was pretty scary. And then there was the Night Sisters.
Rebels has those spider things as well.
In the movies, Vader himself can be considered a horror-esque character (they give off the whole slasher feeling in Rogue One).
So yea, I believe horror can work in star wars in small doses, but dont try to make a whole Horror movie in the Star Wars Universe unless its done really right.

Horror has been done is Star Wars before. While it's mostly about heroic endeavors and all that jazz, there was a story about zombies. They were called Death Troopers. I haven't read it, but I know it was about some zombie virus that infected Imperial soldiers aboard a ship.

http://starwars.wikia.com/wiki/Death_Troopers

Ah yes Death Troopers, I recall browsing that book before. Chewbacca and good old Han are in it. I won't spoil it but there is a good ending to it. There was even a trailer to promote the book on YouTube:

@guan12 i didn't know that made a youtube video to promote the book, that was awesome, makes me now want to read the book, thanks for sharing that!!

visit the sewers of Corucant and you have your answere

but a lot of lore regarding fearindusing creatures or sights

I think star wars and horror can defiantly work well a good example of this is star wars clones wars tv show when they go back on geonosis and find a cave filled with undead geonosians who are controlled by bugs. that episode had major horror elements and inspirations that of alien mixed in with some claustrophobic scenes. If they were to adapt horror on star wars movies i think it would be fantastic.

So I've read Death Troopers (loved it) and did some digging.
While Death Troopers from the novel aren't canon they're recycled into Rogue One's Death Troopers.
The novel is non canon but they changed those Death Troopers into Undead Troopers (Zombie Stormies) who are actually canon.

https://starwars.wikia.com/wiki/Project_Blackwing
https://starwars.wikia.com/wiki/Undead_Trooper

So while we won't be seeing it on the big screen anytime soon, horror is present in numerous forms in the Star Wars verse and frankly it works perfectly:

• Geonosian Brain Worms
  
• Undead Nightsisters
  
• Undead Sith Warriors
  
• Zombie Troopers
  
  As it has been stated Vader is pretty much the essence of horror Galactic Empire era, even in some cases comic artists drew his helm to be more skull shaped.
  

Of COURSE horror can exist in Star Wars, I mean have you seen The Last Jedi? Truly a horrific sight...

I'm kidding, personal preference and joking aside, I'm a huge fan of horror in media. I think horror could work incredibly well in star wars. Space is a fantastic place to put someone in such a vast infinite world, but also make them feel a complete sense of solitude and hopelessness at the same time.

Just because the overall idea of star wars now is family friendly (Especially with Disney holding the cards which is..meh imo.) doesn't mean you can't master an atmosphere of horror within the lore.

It could be as simple as a psychological horror dealing with the mind manipulative ways of a sith lord to a struggling and singled out padawan in the dark emptiness of space. Psychological horror is one often skipped over because most just want the general "ah spoopy stuff splashed on screen all time" method. Or as has been mentioned, Death Troopers, would work fantastically.

I can see the argument for the fact that Star Wars is a bit Epic Fantasy Space Opera, and one of the main reasons a space horror works, is the grounded aspects of technology and the universe. Like Alien, Dead Space, etc. However, if done well, could mirror a Alien/Jason/Halloween vibe. A group of traders or smugglers lost on a derelict scrap job now being hunted by an old ancient sith. I always remember that one moment in KotoR 2, Darth Sion's first introduction. The power failure on the ship, the dead crew around him, and his slow walk towards you down the blinking corridor. Now of course the way it was presented was a mix of tension and "holy crap this guy is bad ass" feeling, but that's sort of my point. He's practically a zombie anyway, holding his body together with the sheer will of the force.

All just my opinion though.