To measure a thermistor, you need an accurate current source and something to digitize the resulting voltage drop across the resistive element. The 6211 cannot do the former. It could do the latter, with its accuracy depending on the accuracy of the 6211's AI (not great). You'd also have to control the thermistor's position near the cold junction compensator and, ideally, isothermally isolate it, which would involve building some kind of enclosure. Even with all of that, you're going to have several degrees of measurement inaccuracy before also including thermocouple and thermistor measurement inaccuracies.
It would be way easier to just buy a DAQ device that is designed to measure thermocouples with built-in CJC compensation. These devices will have an accuracy statement for the entire measurement solution. You just have to add the error of your thermocouple. If you're looking for an NI solution, the TC-01 is a single channel, cheap device. You could also use a single slot cDAQ like the 9171 with a thermocouple module (9211, 9212, 9213, etc.) if you need multiple channels.
