Green Hills is not targeting the super-tiny, severely resource-constrained embedded microcontrollers with their INTEGRITY OS or MULTI IDE, so in their market they wouldn't get very far if their proprietary C++ compiler didn't support STL or a heap in general. The following web pages seem to support this:
http://www.ghs.com/news/20030915_m40.html
http://www.ghs.com/news/20041116_mobileye.html
So I'd say "Yes, you may use std::string, std::map, malloc(), new, etc."