I was hoping that but the documentation (as of 10.x/11.x headers) seems to give only these choices
| ASAtom value | Operating system |
|---|---|
| FSRefWithCFStringRef | Mac OS |
| FSSpec | Mac OS |
| CFURLRef | Mac OS |
| POSIXPath | Mac OS |
FSRef (pathName object must exist) | Mac OS |
CString | Windows/UNIX |
And the CString (sometimes Cstring in names eg ASPlatformPathGetCstringPtr) returns a platform path in non-Unicode format (char *, does not seem to be any way to return a WCHAR* value).