I think variables in the static:: namespace are only sync'd across the TMM's during RULE_INIT. Any changes to the static:: variable in RULE_INIT should work fine. Changes to static:: variables after RULE_INIT won't be synched. Checking if the static:: variable exists should always work (assuming you're not unsetting the variable in a rule). If you're using true global variables, then the VS should be demoted automatically from CMP and only run on one TMM instance.
As Naladar suggested, if you're seeing that 'info exists' test fail, it would help if you could post the iRules you're testing with. You could also open a case with F5 Support to investigate the issue further.
Aaron