Lots of people know, and have tried C++. For example there are gtkmm (C++ bindings) for Hildon out there, but somewhat sub par AIUI. There have been numerous threads on maemo-developers about it, including one today.

The Maemo 2.0 (Mistral) roadmap mentions making it easier to use other languages such as C++:

http://maemo.org/platform/docs/roadmap.html

HTH,

Andrew