Hello Wen How,
General speaking, yes, it is fine to use IPP and OpenCV library together in a sample project or *.cpp file.
Both of them can be used independently if latest OpenCV version (i.e OpenCV 2.1.0 default build without USE_IPP option. )
You may find some sample code and discussion from Using Intel IPP with OpenCV
Intel IPP Support Model Changed In OpenCV 2.1
and Intel Ipp - Open Source Computer Vision Library (OpenCV) FAQ