Yeah, I just discovered that the "groups filter" was a simple text search box. I've been feeding it AD/LDAP filter strings for a while with no luck. Kinda poor terminology there (or maybe it's just me being obtuse).
About the plugin. I think my problem may be an old vCO installation that's causing problems. In the vCenter web client, if you go to Administration > Client Plugins, there's an Orchestrator plugin listed. I'm just not sure if that's normally part of vCenter or if it's added during a vCO deployment. Since I removed all the vCO extensions, I'm wondering if I need to remove that plugin too.