If your playing over a G7 chord could you use D dorian?

No. Avoid using a D dorian over the G7

Well, D dorian has the exact same notes as G mixolydian, which is the most basic scale to play over a G7 chord. So I'd say yes, those notes will work great over a G7 chord.

The only note to be careful with here is the C. It works perfectly fine as a passing tone or neighbor tone, but won't sound very good when held over a G7 chord, since it clashes with the B in the chord. You can play a G7(sus4) chord instead, which replaces the B in the chord with a C. In this case, it's just the opposite; C works fine, and you have to be more careful when using the B note.

As the previous answer says, the natural scale for G7 is G mixolydian, with the same notes as D dorian. However, anchoring your melody to an imaginary D minor chord, instead of the actual G7, will give a very different feel. whether it soars or seems subtly out of tune all depends on the exact musical ideas you have; it cna work or it can fail, it is down to you.

You noodling?

Follow the harp (harmonica) player's rule, play cross or bent.

G7 indicates key of C, bent is a tone below the tonic, play in Bb dorian, Cross is a fourth above the tonic, play in F mixolydian. Pentatonic F dorian would also work (that's bent on G).

But D dorian would work best in E, although pentatonic D dorian is an "escape route" over G7, since Em is the relative minor to G.