I just did a short test.
I did not use your sources, but hacked the relevant part into the IncrementalSearch-plugin.
The event gets triggered, but wxBell does nothing (on Fedora 20 64Bit).
RequestUserAttention shows a notification (on gnome-shell), but only if C::B is in the background (as documented).
If I find time, I will clone your repo and do another test.