Good point, André. I missed the "must" in those rules. And I totally agree with setting DRS to manual before enabling those rules, particularly since he seems interested in avoiding a mass migration. Being able to preview the DRS recommendations prior to implementing them will bring the peace of mind he seems to be looking for.
Another alternative to avoid a "vMotion storm" would be to only add a few hosts at a time to the non-production critical VMs group, let those migrate, then add some more. This would allow a more controlled migration.