I got it to work (minus sound) on 8.2 64-bit right now. Basically, you need to install a list of ports, and copy the included libraries to /compat/linux/usr/lib . Something like this (assuming you have security/sudo and ports-mgmt/portmaster installed):
sudo portmaster -Bd linux-f10-alsa-lib linux-f10-atk linux-f10-cairo linux-f10-expat linux-f10-fontconfig linux-f10-gtk2 linux-f10-jpeg linux-f10-pango linux-f10-png linux-f10-sdl linux-f10-sdl_image linux-f10-tiff linux-f10-xorg-libs linux-sdl_ttf linux_base-f10 linux_dri
cd dwarf_fortress_directory
sudo cp libs/lib* /compat/linux/usr/lib/
If you use the binary nvidia driver, I think you can/should? skip linux_dri in the above list ... test and see, really.
As for ports: Porting it in the classic sense should be very easy: In the best case the only thing needed would be to change some include paths for the libraries used. There might be some fun with ALSA (FreeBSD uses OSS natively), though using the SDL sound libraries would fix that, or I think there is a beta-quality userland ALSA-for-FreeBSD thing available.
Porting in the FreeBSD sense shouldn't be too hard; it would basically be a case of setting the above dependencies (and whatever else I've forgotten because I've already got it installed), and probably installing it to the usual locations (bin, lib, etc) within /compat/linux/usr/local (though I guess we could just dump it in local/dwarf_fortress/ ).
(A FreeBSD port is a few text files with the info needed to download, extract, compile if needed, install and uninstall something.)