Slaughterhouse Five presents elements of science-fiction and satire, but is most often categorized as literary fiction. This is true for several reasons, the most prominent simply being Kurt Vonnegut's status as a great prose writer with serious intentions.
Satire is not usually used as a genre description when it comes to long form fiction (which, to some extent negates the option of categorizing this book as satire).
Furthermore, though this novel certainly satirizes many aspects of the cultures of America and of war, the novel also clearly offers an alternative to the things it criticizes and satirizes. The presence of an alternative, removes the book from consideration as pure satire. The alternatives or non-satirical elements here are exemplified by the narrator's rusting guns, his advice/mandate to his sons to never glorify war, and his stated indifference to people in general.
In other words, there is quite a bit of direct honesty in this novel, which counter-balances the satire label. If a book is not one hundred percent satirical, we can't catergorize the work as a satire.
Considering science-fiction as a genre description for Slaughterhouse Five leads to questions of plot. For a novel to be a science-fiction work, there should be a real emphasis on plot and resolution, both of which are relatively minor concerns in Slaughterhouse Five.