I've reproduced the problem (with OpenCV 2.4.9). A workaround here is to disable OpenCL from OpenCV build. But it is strange that the standalone rtabmap libraries can be compiled without problems. It may have a difference with the compiler options between the standalone and catkin builds. Another related post here.
I tested again and I've modified the rtabmap_ros CMakeLists.txt to explicitly look for OpenCV and set the its libraries found before linking to catkin libraries (which indirectly include OpenCV binaries from cv_bridge). Normally, no specific requirements should be taken when building OpenCV (no need to disable OpenCL). It should be installed in "/usr/local" though (default install path), to be found by the package before the binaries installed in "/usr" (the PATH should have /usr/local/bin before /usr/bin, which is already the default).