Personally, I don't really hear the deep purple influence in Viper King, aside from the fact that Deep Purple used a lot of organs in their sound, and this song is very organ driven. I made the Highway Star comparison purely based on the subject matter, and what it represents for the band, in other words, being their driving song, and I'm quite sure that James LaBrie made the comparison for the very same reason, and not because of the general sound.
With Divine Addiction, I can definitely hear the Purple influence in the sound. But from what I'm hearing, it's not about driving a car, is it?
So yeah, it's kind of a moot comparison either way. The point is, Dream Theater now has a fun, bouncy, driving anthem that you could throw into a playlist with the likes of Radar Love and Born To Be Wild.