You've asked a very interesting question here. The short answer is what you've already observed: "Yes or no, depending."
Longer answer, depending on "what"?
Most people don't like *fast* harmonica playing in bluegrass. It's very hard to do, and sounds very hard to do, but I personally don't usually like it, and all the "huffing and puffing" as I think of it, distracts from the pure sounds of the picked and bowed instruments. Flatt & Scruggs and Jim & Jesse both experimented with harmonica players, some of the best in fact, but many fans didn't like it, and with those two high-profile experiments, most people consider the case closed.
**However**, on slower, wistful tunes, I think a harmonica can add a beautiful, evocative feel that is not at all foreign to the sounds and emotions of bluegrass.
I am a bit biased here, because my dad played harmonica. After rejecting him as a music partner as a teenager (par for the course, I guess), I later "rediscovered" him, and had many happy times making music with just banjo and harmonica. We even did a little bit of recording that I'd like to release someday.
In jam sessions, I'm always willing to give a harmonica player a turn, just to see what they can do. If they can handle the music well (even in huff/puff style) I'll think of them as welcome, because in a jam, when it doubt it's better to be inclusive -- usually, at least.
So I'm just underscoring your experience and the conclusions you've already drawn:
1. Some people will like it, some won’t.
2. Choose where you're welcome, and leave where you're not.
3. To be more generally welcome, bring and be able to play another, more wanted instrument.
Here's a further suggestion:
4. Choose your situations carefully. Don't bring out the harmonica until a slower song comes along, then do your thing, with good tone and feeling, no histrionics. That will create a great first impression and good reaction. Then put it back away until the next opportunity where you know it will go over well. Don't start "chancing" using it on more questionable songs (especially faster ones) unless you really think it will work. Like a lot of things, a small portion will go over a lot better than a large portion.