Which FUSE ESB and FUSE HQ version are you using? If you are using FUSE ESB 4.3 go to FUSE HQ 4.3 dashboard and Browse resources and select FUSE ESB instance (servicemix 4.3.x) and click on "Inventory" tab and at the bottom of the page click on Edit button to update JMX configuration and on next screen put smx/smx as JMX username/passoword and click "ok". This should resolve you problem and you will be able to view all the stats after next collection interval.
Yes, JMX configuration was an issue in my case. Due to port conflicts I had changed the default JMX port of Fuse ESB from 1099 to 7001. After changing the port information I was able to monitor the service assemblies.