The density of material in the interstellar medium is inferred from (i) the electromagnetic radiation it emits; (ii) its effect on electromagnetic radiation passing through it. Often these approaches are combined to learn about different "phases" of the interstellar medium - e.g. hot, cold, high, or low density, ionised or not.
For example, we can learn about how much atomic hydrogen there is using 21 cm wavelength radio emission. Molecular gas can be traced by molecular emission lines in the infrared. X-ray and particularly EUV emission is absorbed by the interstellar medium. UV and optical absorption lines can be seen in the otherwise featureless continuum spectra of hot stars. The spectra of stars are reddened by dust scattering, etc.
All the interstellar material probed by these techniques relies on an interaction with electromagnetic radiation. So technically, none of it is dark matter and the technical answer to your question is no. Most of the dark matter in the universe does not interact electromagnetically and the density of such matter is inferred solely by monitoring it's gravitational influence.
I suppose what you are asking, is could there be ten times as much "cold" interstellar medium as we thought and could this account for the rotation curve of our Galaxy?
The answer to that is also no. Even cold dust or gas is not cold enough to emit no radiation - we would observe it in the far infrared and microwaves. Equally, a factor of 10 just wouldn't do it. The interstellar medium forms a small fraction of the total mass in the Galactic disc (about 30% - Chabrier 2001) and thus only 2-3% of the total inferred Galactic mass; and it is highly concentrated towards the Galactic plane and centre. Explaining the dynamics of the Galaxy requires a spherical distribution of dark matter that extends well beyond where the bulk of visible material is found.