Sorry no one has replied to this post before and I don't know if you ever managed to figure out how to get nethack running the way you want. I think what you're looking for is the CP437 character set which looks like this (
https://en.wikipedia.org/wiki/Code_page_437#/media/File:Codepage-437.png).
You can accomplish this by using Putty to connect to NAO and configure putty to use the CP437 character set. The manual for putty is here (
http://the.earth.li/~sgtatham/putty/0.52/htmldoc/Chapter4.html). Just do a CTRL+F and search "CP437" and it will tell you how to configure putty to use that character set. Once you've set this up, you can save this as a profile and skip this step in the future.
In your Nethack configuration file, you need to have "OPTIONS=IBMgraphics" somewhere in there. Once you've done this, you're good to go.