Sorry I'm a little bit confused what the exact issue is.
If I read thru all the posts it looks like that SNMP is working (status in devices is correct) but the view in EMC > wireless doesn't show the correct status and graphs for the controller.
If that is the case it sounds like a problem with the langley tunnel between EMC - controller.
EMC needs this tunnel and ssh access to the controller or it wouldn't work 100%.
Also make sure that stats collection is enabled.
If you take a look in the following thread - my 2 posts explain the required settings.
If that is correct and didn't solved the issue I'd delete/add the controller in EMC to see whether that has any effect.