Can dark matter decrease the Jeans length? I am wondering if there are any models of interstellar cloud collapse out there which take dark matter into account. 

If dark matter has local perturbations or density fluctuations, then that may be a large enough effect to cause collapse of an interstellar cloud. This might increase the mass and density of a cloud enough to overcome the kinetic energy of hydrogen atoms leading to collapse.

Are there dark matter density variations at the scale of interstellar clouds?
This is an area of active research. The current Cold Dark Matter (CDM) paradigm predicts bottom-up formation of halos, whereby smaller halos coalesce in to the larger halos we observe indirectly today through X-ray measurements of clusters. This suggests that small dark matter halos wouldn't survive to the present day.

There has been research in to the possibility of mini haloes surviving, but interactions with dense baryonic structures, such as stars, as well as streaming by an irregular galactic potential tend to wipe out any small overdensities in the distribution.

However, if such mini haloes did exist in the early universe they could have contributed to the collapse of primordial gas to form Population III stars. Simulations have been carried out to investigate such a model, with Population III stellar masses comparable to those expected $(\sim100 M\odot)$.