IR imaging is good up until about 4 microns, after that atmospheric absorption gets in the way. One of the bigger issues is that if correction. Most refractors don't have the correction over such a wide pass band to make any use of it. Not sure how the Sloan filter set would do as it is heavily for NIR galaxy imaging (think 2dF survey).
At 4 microns I don't think ordinary mirrors have issues but I know past that gold plating is used to significantly help with reflectivity in the IR region.
As for the refractor vs reflector debate, a refractors will probably always be better for wife field imaging. Short focal length reflectors are either cheap and flimsy in comparison or CRAZY expensive due to their complex optical designs.
A new FSQ106 is not cheap but building reflector with remotely the same performance would be significantly more expensive
And in spite of all that, check this out.
Horsehead IR