I think I've only visited one Orcish stronghold and they were all hostile to me. Are all of the strongholds hostile?

There is one Orcish fort I've been to if that's what you're talking about? it's to do with a daedric quest

Yeah Cracked Tusk Keep. Maybe they were hostile towards me because my character is a Breton and they remember what our people did to their people...

Theres another one if u talk to the book keeper in the college of winterhold after doing sum quests he will mark it on the map

I went to one stronghold where the orcs were hostile but another where they were friendly. I believe you have to do a quest for an orc in a nearby town to get friendly since completing a quest for an orc blacksmith had her say "I'm thankful for what you did. I'll be sure to tell the nearby stronghold you're a friend"