| Em7b5 would be G Melodic Minor, you are correct. Whereas E7alt would be F Melodic Minor.
If you want to use melodic minor harmony with the half-dim chord, then you're looking at the 6th mode of the melodic minor. So Em7b5 corresponds to G Melodic Minor.
Another option would be E Locrian.
Now your A7#9 chord - if you want to interpret that as an alt chord, then yes, Bb Melodic Minor would be appropriate, as the altered scale is the 7th mode of the melodic minor. So, an A7alt chord would go with Bb Melodic Minor.
On the other hand, since the #5/b13 isn't specified in this case, you could view this as diminished scale harmony. The difference being, you would have a natural 13th (and perfect 5th), whereas with the altered chord you have a #5/b13.
So you could play an A half-step/whole-step diminished scale over this chord. The difference between that and Bb Melodic Minor (or the 7th mode thereof) is the F#.
Either scale should work. If the next chord is D Minor, you might favour the altered scale, because it has the F natural, whereas the dim scale has the F#, which is the major 3rd of D - which might not be what you're looking for.
Or on the other hand, it might be just what you're looking for...
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