langway suggested to map WMTInt8 to a byte,
however, I would advise against it.
Consider this code:
typedef char WMTInt8;
WMTInt8 myChar = 'a';
If you translate this as
byte myChar = 'a';
It will not compile until you insert cast statements.
(error CS0029: Cannot implicitly convert type 'char' to 'byte').
IMHO, It's better to bite the bullet, forget about type safety of 'struct WMTInt8' and translate a WMIInt8 as a C# 'char'.
: C++ to C# conversion (and translation to VB