In my experience here (and I have been around a while), the actual case is that some humor is welcome here. But the subset of what is welcomed on HN, versus the set of "all things someone finds humorous", is pretty small. I've had humorous comments upvoted before, even highly so. But there's a pretty particular brand of humor that seems to work here. And you can't always predict how something will be received.
I will say this: some of my most highly upvoted comments are among some of my lowest effort ones (eg, something like "Fuck these guys. The NSA can go go hell" or similar) while I've had tons of comments that I spent half an hour or more working on, doing researching, finding citations, etc.... and they either got zero votes, or got downvoted.
My point is that it's really hard to guess how people will react to any particular comment here, humorous or otherwise, on any particular day.