Yes. Bluetooth audio on the Spark amp is not definitely not limited to Spark app only, so you can use Spark amp as a normal Bluetooth speaker that gives you awesome guitar tones at the same time.
However, if you wish to take advantage of the Auto Chord feature in Spark app with the songs you’ve saved in Spotify/Apple Music, definitely check out this link on how to import your Spotify/Apple Music playlists into Spark app.