I'm missing something?
Code::Blocks currently have support for developing with these compilers:
- GNU GCC Compiler
- Microsoft Visual C++ Toolkit 2003
- Borland C++ Compiler 5.5
- Digital Mars Compiler
- OpenWatcom (W32) Compiler
- SDCC Compiler
If you are talking about compiling the Code::Blocks IDE itself with OpenWatcom, that currently will not work out-of-the-box, because the only compiler tested for compiling it itself is GCC.