1. Start Extreme Management Center.
2. Change to the Network -> Devices tab.
3. Right click on the device in question and select Device > Refresh (Rediscover) device
4. Click the Yes button.
This will re-read the information from the switch - specifically the NetWork Monitor Cache information which will contain interface information. There is a default of 12 hours between updates if this table -- so the ifAlias should eventual populate on its own.
The Network Monitor Cache can be adjusted from Administration > Options -> Network Monitor Cache.