A long time ago, I wrote several blog posts which related to Ubiquiti devices, especially monitoring using Cacti rrdtool-based graphing solution. These are probably obsolete now, but someone has pursued this idea further...
Related blog posts
Solution
Please read Cacti - monitoring ubiquiti and mikrotik forum thread (original link) and download ubntcacti-ap-trzepak.py.gz Python script.
Notice, that I do not have access to Ubiquiti devices anymore.