A friend of mine told me that the usage of scales or modes in jazz music is not common. Even I heard myself in a Miles Davis interview that jazz is a tradition. So here are two questions basically: Is it common practice to use scales (modes) for jazz improvisation? Was is practiced back in the swing era, unlike the modal jazz "era"?
Is it common practice to use scales (modes) for jazz improvisation?
TL;DR: Yes, of course it is.
For the start of the song, you have a melody and some chords to accompany it. After the melody has been played, the musicians start improvising solos. In order to see what are they going improvise on, they study the chords and the melody. These two belong in some certain scale(s) (usually more than one). So, when they realize what is (harmonically) going on in the song, they start improvising on top of the modes that belong in each chord, or in a scale the chords belong in.
For instance, pretty much all the jazz songs have the ii-V-I, like Dm7-G7-Cmaj7. In a cadence like that, you can improvise on C major or if you are bit more skilled, you can follow the chords and play the respective modes: D Dorian- G Mixolydian - C Ionian.
If you at the questions on this site tagged jazz you'll see many instances and queries concerning the modes/scales played in jazz.
The difference between modal jazz and jazz preceding that era, is that before modal, the musicians used chord progressions, while in the modal era, they used modes. If you listen to Miles Davis's So What, it has the same AABA form, but you won't see a chord progression there. You'll notice that the A is just D Dorian and B is Eb Dorian and that's it. Swing ear musicians didn't use this way of composing; they had chord progressions.
I've seen this quote from Charlie Parker in many places...
"I was working over 'Cherokee' and, as l did, I found that by using the higher intervals of a chord as a melody line and backing them with the appropriately related changes, I could play the thing I'd been hearing. I came alive."
The part "higher intervals of a chord as a melody line" catches my attention, because they are Parker's own words and pretty clearly indicate melody line from chord tones. Sure, he didn't say "I don't use scales." But, it's ridiculous to even think a musician would think in that way. If you are trying to weigh chord tones versus scales, the gist of Parker's quote seems clear enough: chord tones are central.
Also, it's pretty obvious that filling in a seventh chord with passing tones results in a scale. So, are scales derived from chords, or vice versa? I don't think you will get far trying to place one over the other. You obviously need both even if a melodic line is essentially derived from chord tones.