Spotlight builds up the list of keywords from the file schema.strings
located
/System/Library/Frameworks/CoreServices.framework/Frameworks/Metadata.framework/Resources/English.lproj/schema.strings
Mail.app calls the read/unread column "Message Status" (although it's not shown in View->Columns, only in View->Sort By). It shows unread status but also other things, such as if the message is a Note/Todo.
I've had a look through the schema file for anything related to message status/read/unread and nothing turns up, so I have a feeling that it's not supported out of the box. However third party software can supply it's own schema.strings file (eg Adium does this), so it's possible that one could edit the file, or supply a new one containing the appropriate keyword mapping to add this feature, though I'm not sure how.
So the short answer is unfortunately no - at least as of Snow Leopard.
Why are your examples straight from the Google mail help? – Daniel Beck – 2010-09-22T06:07:20.657