I hunt Unit 1 and 4 mostly. Kupe is Unit 3. We had a record breaking snow winter in 2005/06. Deer got hit everywhere pretty hard even down towards Petersburg and Wrangell. They are rebounding quite nicely. Winters are always what control the population, not hunting pressure.
If you can get over Kuiu, the next island to the west, I'd try that. It's been logged over pretty good, but lots of road access and big bucks. Consider getting a black bear tag too. Don't know that much about Kupreanof. Moose are actually wandering out onto the islands. If you can hunt during the rut [early to mid-Nov] I'd say got for it. Get a good deer call. Maybe your buddy has one. It's fun to call 'em in.