not any QZA, mind you. There are specific types that are transformable to Metadata... but most types can transform (either as sample or feature metadata, depending on the file), and FeatureData[Taxonomy] is a type that can be viewed as Metadata.
If you ever feel like some data type would be really useful as metadata (e.g., for filtering or tabulating) but you're not sure if it is transformable, just try using it and QIIME 2 will tell you if you've done something objectionable!