If a guitar riff is in the natural minor scale, then will the chords be taken from that same scale?

Question

If a guitar riff is in the natural minor scale, then will the chords for the same song be taken from that same scale, and visa versa with the major scale, will the chords be taken from the major scale?

Plus, does the vocals range in the same scale as the chords and riffs?

Best explanatory answer gets 10 points...

Answer 1

Example of chords in Am, starting with Am

1 - Am

2 - Bdim

3 - C

4 - Dm

5 - Em

6 - F

7 - G

8 - Am

And from the corresponding C major

1 - C

2 - Dm

3 - Em

4 - F

5 - G

6 - Am

7 - Bdim

8 - C

Notice how C and Am are effectively the same scale? (any major key has a corresponding minor key if you take the root 3 semitones lower)

Answer 2

This is sort of a complex question.  You have to analyze the key to see what fits.  

So say you are playing a A Natural Minor Scale:

A, B, C, D, E, F, and G

So your chords will be based on those notes.  The easiest way is to refer to it's relative Major, which will be the 3rd tone in a Natural Minor scale.  

So C Major are the same notes.  C, D, E, F, G, A, and B

In a Major scale, the 1st, 4th, and 5th note are Major Chords.  The 2nd, 3rd, and 6th notes are Minor Chords.  The 7th is diminished.  So you know in the Scale of A Natural Minor you can play:

C Major, D Minor, E Minor, F Major, G Major, A Minor, and B Diminished.

Where this question gets complex, is considering Minor Scales that are not natural such as Harmonic.  The Harmonic Minor raises the 7th note.  So the A Harmonic Minor is:

A, B, C, D, E, F, and G#

This throws what we were talking about for a whirl.  The standard chords could fit, but could aslo not fit too well.  You'll need to analyze what the G# did to the scale.

The A minor chord uses A, C, and E.  So we are ok there.

The B Dim uses:  B, D, and F, so we are ok

The C Major uses:  C, E, and G.  So the G might not sound too great, so maybe play a different C.  Such as C, E, D

The D Minor is:  D, F, A

E Minor is:  E, G, and B.  so we might have to tweak this one.

See how it works?  You need to analyze if you start using some of the different minor scales.