I don't know - which parts of FreeNAS' functionality are you looking for? For example, using vnstat, you can gather information about your bandwidth usage and output it to generated web pages.
FreeNAS is kind of a specialised system, so it's hard to make an Distro to function exactly like it. (Also remember that FreeBSD and Linux are two totally different kernels)
EDIT: Ok, after checking out FreeNAS, I figure it's possible, but you'll probably need to write the whole web interface yourself.