I can prove you 100% that packet injection is working with wl1251. You may know that I have developed the monitor mode patches for wl1251. Some time ago Neopwn asked me to develop packet injection patches for Backtrack Mobile, which I have done at least of my knowledge successfully. There may be some testing and cleanup needed, but the basics are working pretty well.
My current intention is to get a full-featured upstream wl1251 driver in the linux kernel, so compat-wireless can be used as full replacement. Currently it lacks some features which are included in the Maemo Fremantle version.
I also want to note that I am currently not in the position to give anyone access to the packet injection capable driver, because I developed it exclusively for Neopwn.
Furthermore I have recently talked to Neopwn and he is currently working to reorganize the project so he can accept contributions, but that will need some time.