Paint can crack for many reasons, such as you stated, or bad body work (bondo), structural flexing of a body panel.
You should try your best to determine why it cracked before attempting a fix, or more than likely it will return.
Yes you can sand (feather) out the crack and reshoot the hood. However if you have metal flake in the paint it will be hard to blend in the repair. If you have enough paint I would re-shoot the whole hood.