Last time I was doing any modding for Morrowind a couple of years ago, the only version of the .nif exporter for Blender was for an old version (even at the time).
I'm wondering if it's seen any updates since.

It's great to see that the modding community is still going strong, by the way!

edit:
As an additional question, what's the best site for hosting mods nowadays? I always liked PES as you didn't need an account, but apparently it's been having some issues.

You didn't need an account for downloading, but you couldn't upload your own mods without one, which is kinda obvious. Morrowind Nexus would be my choice.

As for the Blender, yes, 2.49b is the best, which is an old version. You can work in a newer one, and then import in 2.49b for exporting into nif though.