Comprehensions such as for/list and for/hash are polymorphic, in that they operate on arbitrary sequences, of whatever type. for/list constructs lists; for/hash constructs hashes. Clojure, a language that takes uniformity of interface much further than Racket, has similar operations.
You're completely right on the math. I had math-oriented types wrong; I assumed that the author wanted the ability to say, "This type is restricted to values defined by this set," which he didn't. Even if he did, I see that Typed Racket actually does support such types, which is awesome. So I'm completely wrong.
Whether e.g. #hash((key . value) (key . value)) counts as a literal hash syntax is interesting. If you want to argue it does, then I'll argue that C does, too, since I can trivially #define my way there through C99 struct assignments and a function that constructs a hash off an array of those structs, or that C# does because I can use an initializer (e.g., "new Dictionary<string, string> {{"Foo", "Bar"}, {"Baz", "Quux"}}"). Literal hashtables and vectors, to me, means something that's visually apart from base syntax forms, specifically so that it stands out to the coder. By this standard, Python, Ruby, Smalltalk, and Clojure would qualify, while Racket, Io, and C# would not. Whether that matters to you depends on what you want.
I don't think that's right about hash tables. In particular, the distinction I would make is that literal hash tables are part of the syntax of the language in Racket, like in Clojure, Python, etc, and not in C# or C. What this means in Racket is that (read (open-input-string "#hash()")) produces a hash table -- that's parsing, not running the hash table constructor.
You might not like the literal syntax for maps in Racket, but it certainly exists.
Typed Racket has lots of math-oriented types; we just wrote a paper about their design here: http://www.ccs.neu.edu/racket/pubs/padl12-stff.pdf
Comprehensions such as for/list and for/hash are polymorphic, in that they operate on arbitrary sequences, of whatever type. for/list constructs lists; for/hash constructs hashes. Clojure, a language that takes uniformity of interface much further than Racket, has similar operations.