They seem to mask u32 values just fine everywhere, so u32 being larger than it has to is no problem.
ulong is as you know the smallest type that's always guaranteed to be at least 32 bits.
ulong is as you know the smallest type that's always guaranteed to be at least 32 bits.
Additionally, char is required to be at least 8 bits by the C standard, but tweetnacl assumes exactly 8. Some oddball architectures have larger character types, but POSIX mandates 8.
[1] http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf
[2] http://nepsweb.co.uk/langstand/isoC/gordon/ansi-c89w.txt
Do you have the section number in the latest freely available C99 working draft? The "Types" section (which 6.something in the draft) simply says what I said earlier about scalar rank. And 5.4.4.2.1 doesn't seem to exist in the draft.
I assume the intent of tweetnacl is to be C89-compatible, but due to the long long (and char, although that one's pretty pedantic) issue there's little guarantee of success.