No addons actually require windows. All wow addons are run as lua scripts from within the WoW application. This is a platform independent system. All code, directories, and output files are the same cross platform.
The applications that require .net / windows are simply running windows programs that scan the addons directory for data saved in text files and either process this, or upload it to a website.
If you have parallels all you should need to do is run WoW in Mac OS X and run the processing/upload windows app in parallels. The only tricky part would be ensuring that that the windows app can see the WoW directory and has the proper permissions on it.
Many addons with .net upload components have web scripts or at minimum instructions for uploading/processing addon data manually. (I know ctprofiles/eqdkp/WoW web stats/most of the popular addons) offer this.
Lastly if the addon you are looking at does more than parse and process addon logs automatically, (ie "addons" that actually control/automate your character) chances are it is illegal and can get your account banned.