Recommendation is to use the Custom Property Manager to create a Custom Property at the Node level and assign values to that Custom Property in order to group the nodes by Custom Property value instead of by Node Group.
Custom properties - OK. So I have to create a new custom property and then manually edit batch-add it to my nodes. Luckily, batch editing is there.
Thanks stripet!
P.S. Solarwinds, seriously? Can't make an alert based on existing grouping?
P.P.S. The trouble with custom properties is that it's much more rigid, restrictive than grouping or tagging. A node can belong to multiple overlapping groups ("WinServer", "Blade", "HP, "Proliant", "BL460c G7", "Encoders", "Telestream Episode", "Systems that crash too much"). Sure I could use or create a separate custom property for each ("Hardware type", "vendor", "series", "model", "core purpose", "core application", "free form") - and then find myself entangled in a mess I create myself. Tracking nodes by tags or group memberships would have been so much easier.