Can you search documents on your iCloud Drive using Spotlight? Probably, but it doesn’t seem to work using normal metadata indexes.
mdworker
When you keep documents in iCloud, are they backed up in Time Machine, searched in Spotlight, and kept securely?
Don’t you want to search your backups? Like it or not, Spotlight will still index them, even if it doesn’t tell you that it is.
The Eclectic Light Company 