Hello,
you see [object Object] because cm:creator is a complex object containing the user, first and last values. Unless you provide a custom renderer, this will not change if you attempt to render cm:creator directly.
For your owner example please keep in mind that this property is usually not set, except you have some actions that reassign ownerhsip. If you were to use the same approach for the creator, it should work.
Regards
Axel