If you can't rely on the Galactopedia, rule book, and patch notes then we're just guessing.
I blockaded a homeworld, and a colony as Gizurean. If Gizureans aren't hostile enough then idk.
Well, there is always the matter of seeing what happens in the game. The best patch notes are incomplete or just plan wrong in some cases. Rules and manuals are less complete than patch notes. And even the best system that is not trivial got bugs.
In DW I am quite sure that blockading ships never shoot at ships. Shooting is about war between empires (or pirates), and blockading ships are usually not at war (well, mine are). If they do shoot at someone, the reason has no relevance to the blockade status, apart from the blockade keeping them there.
I have at exactly one time seen a blockade work just fine. But it is hard to actually see, because you both have to pay attention to the little things, and have the situation happen. In my case it worked so well that I consider it an AI failure.
Spaceport A was blockaded. Spaceport B was "further away from the main empire".
Spaceport B had a shortage (resource situation was probably not that great overall). Spaceport A had stuff (and noone was taking it away as it was blockaded).
Spaceport B kept generating transport missions "bring me XXX from spaceport A". Freighters arrived at A and turned away since they could not pick up. Repeat again and again. It would be rather simple for B to get stuff at other places, but in appears it ignored the blockade status.
I believe that you can play a whole lot of games without a situation like that happening to you. And even if you do you have to be able to have enough time to even notice what is going in at a spaceport at the fringes of an empire. The situation includes a somewhat effective AI blockade in a situation where the resource situation is probably a bit strained.
If you really want to see what happens, it could be possible in early game if the AI is kind enough to blockade a key mine. In that case you can even scrap other sources of the same resource. Thing is, I believe this may be somewhat common in legends, I doubt it is as common after the pirate upgrade in Shadows.