I am just writing an adventure around the dwarven and orc history. In my party I have a dwarf and a half-orc (we have not played yet). Reading the Pathfinder Handbook Dwarfes of Golarion it is quite clear that they absolutely hate Orcs. But there is no information about the relation to half orcs. Is there any source with information about it?
There is very little information on this. For dwarves it goes like this:
"We hate orcs!" - "What about half orcs?"
"They are... Half as bad!"
From pathfinder wiki:
Half-orcs are generally considered little better than their full-blooded orc relatives and regarded with suspicion.
From Inner Sea Races (page 72), regarding dwarves, we got:
Dwarves and half-orcs rarely get along, due to the millenia of violence between dwarves and orcs. Many dwarves have difficult seeing anything other than their ancient enemy in half-orc's burly frame, sharp tusks, and green skin.
And again (page 104), regarding half-orcs:
Other humanoids, specially elves and dwarves, have too much hate for half-orcs's orc heritage to even bother remembering the human portions, and react with anything from distain to naked violence.
Also, check the wiki for more info on half-orcs on society. Most of that information was published on the Bastards of Golarion player companion, but the book has stuff not posted on the wiki, like information on half-orc heritages (half-orcs from darklands, half-orcs from the desert or jungle, etc).