The only possible meaning for smoothness that comes to mind is the following: A measure on ${\mathbb R}^n$ is smooth, if it has a smooth density against the Lebesgue-measure.
On a manifold, a measure is smooth if it transforms to smooth measures on every smooth chart.
The question, whether a given smooth measure comes from a metric is equivalent to the question whether its density has a zero or not.
If it has no zero, simply choose any Riemannian metric. Then your given measure has a nowhere vanishing density against the measure coming from the metric.
Simply multiply the metric with the reciprocal square-root of the density to get a metric that induces the given measure.
Since Radon-Nikodym densities are uniquely determined, this is an if and only if criterion.