The units used in your database and reports are irrelevant when it comes to WU. Provided WeeWX was properly installed and your station is correctly configured for the rain collector size you are using everything should just work. The best way to troubleshoot most WU upload issues is to set debug=2 in weewx.conf and then restart WeeWX. WeeWX will now log the data being uploaded to WU. You can now compare the logged data with the archive records being stored by WeeWX or, if you are using WU rapid fire, you can run WeeWX directly (http://weewx.com/docs/usersguide.htm#Running_directly) to capture the loop data being seen by WeeWX to compare with the RF uploads. Of course in your case you will need to do this when it is raining (you could manually tip your gauge but that will irreversibly pollute your WU data - unless you disconnect WeeWX from the internet)
Gary