When you log into the GUI in the top right there is a nice load balancer status box that shows green, yellow, or red. Currently there is no way to poll this status via SNMP as a single OID. Could you please add the overall status as a SNMP value in a future release?
There isn't an SNMP value (or SOAP request) you can use to get the colour of the status indicator.
You can do something equivalent with the SOAP diagnoseSystem() call; the status indicator's colour is calculated by going through the sections of the Diagnose page which can raise errors and determining the most serious error in any of these*. You can get these error states from the Diagnose.ErrorInfo object returned by the SOAP call.
(* the applet status code merges the errors from all traffic managers in the cluster and does a couple of additional checks, but the most significant errors will be published in the SOAP data)
Just remembered this article: Tech Tip: Reading Stingray's internal diagnosis report using Perl and SOAP