I'd say a meteor logia probably does not fit into the logic of what makes a logia. Logia fruits are not about generating stuff and being intangible, they are about becoming something that exists in nature. Intangibility and element generation are abilities granted based on the properties of the element. This is why BB isn't intangible, the element he has just lacks such a property. And katakuri is a special paramecia because mochi does not exist in nature. With that in mind, I think the soot soot being a logia, in the sense of oda classifying it as one, is probably a coin toss.
Soot as defined by google: " Soot is a deep black, powdery substance composed of impure carbon particles, produced by the incomplete combustion of hydrocarbons, such as wood, coal, oil, or plastic.". With that definition soot can occur naturally. But the majority of it would be the result of man made processes. So you can argue it's a logia because soot can appear without man intervention or you could argue it's a paramecia because soot for the most part does not occur naturally.
Oil of course exists in nature so it would definitely be classified as logia. Though it'd be a bit of a lackluster power since fire is such a common power among powerful warriors. An oil logia would just explode and die from a fire slash from zoro.
I think a salt logia would mostly check out. Though it depends on how much salt correlates with water and it's less than friendly properties against devil fruits. Given that salt worked against moria's abilities but not big mom's homies I tend to think the correlation is not too strong and it only worked against moria's abilities because salt is effective against spirits and such.