You can post, but by default no one besides you can see it. To the poster, it just appears as a normal comment. Turn on "showdead" to see posts from hellbanned users.
I had a hellbanned account before this one, and the other thing I noticed is that each page load took forever (10+ seconds) instead of the basically instantaneous loading of my current account. A very passive-aggressive way to annoy someone enough to stop posting in my opinion.
I can confirm that you are NOT hellbanned. One way to see if you are is logging out and see if your comment is still there. If it is not, you are banned.