HMMM. It's tough to say. I Google-imaged "Splash" and here are some pics, this Splash Sumatra has a few really really dark tail feathers, but I don't think they are "true" black:
http://upload.wikimedia.org/wikipedia/commons/b/bf/Splash_Sumatra.jpg
And this Splash Ameraucana hen has a few stray feathers that are very dark blue - but I don't think truly black??? Hard to tell:
http://www.wilkamdai.com/images/chicken_Araucana_SplashPullet.jpg
So, I think it is possible he may be a Splash rooster. Only one way to tell, breed him to hens that have Black tail feathers and no blue, and see if you get any Blue chicks. If he is Splash, all of the chicks will have blue tails. If he is Blue, half the chicks will show Blue, half will show Black tail feathers. If he carries zero Blue genes, then all the chicks will have black tails.
IF all the chicks have black tails - then you truly have something special!!!
Because Blue can make it challenging to see how much white is actually there, I bred it out of my flock for now. The nice thing about Blue is that it's a dominant gene. It doesn't hide, so I am able to add it back to the flock (via a Swedish Flower most likely) whenever I want. But, for now, I prefer to leave it out, so I don't have the confusion of Blue or Splash "faking me out" and making me think I have more-spotty chickens than what I really do have in my flock! LOL. Going to get white spotting the HARD way, and then when I add the "mock white" effect of Splash or pale Blue feathering, these are going to look super-duper spotty!
If you are breeding to increase the amount of mottling on pure Swedish (which would be a great help!) see if you can spy any pure Swedish that have black tails, but still have more white than normal. Oh, and note their ages, the baby Swedish have a lot of white that drops as they mature, and then all mottled chickens gain white as they age. So try to compare apples to apples - look at Swedish roosters and hens at about the same age, like one year old. If you see any hens with black tails and lots of spots, or roosters with black tails and lots of white, and no Blue or Splash genes, please report them here! I'd love to see and maybe try to get their offspring to include in the program, it would be a big help.