Yes, you can overwinter medium nuc's.
The key to beekeeping for me is to propagate, propagate, propagate. . Nuc's seem to overwinter very well; are a sustainable resource to help solve lots of problems in other hives, and could be a financial resource also.
After reading "On the Spot Queen Rearing" and especially after watching Michael Palmer's lectures at the National Honey Show (see Youtube or the National Honey Show web site) I started overwintering 4 frame nucs but I now use 5 frame Nuc's and they are all medium frames -- just to be clear, I make my own Nuc boxes to hold 5 frames - each holds five frames and I try and stack them 3 boxes high. I make them up in late July to early August, about half are with bought queens the others raised their own, and then feed them heavily in September and October.
I prefer to have free standing Nuc's and not he "duplex" type as the duplex only held 4 frames each and the boxes/supers you use are harder to manipulate. I would rather just push two 5 frame Nuc's together if I want to try and share heat from each hive.
These Nuc's tend to over winter quite well - and I am beginning to think smaller hives overwinter better than larger hives, and they really take off quickly in the spring.