It’s a community of dwarves of all clans and together they form the militarized regiment; the Hammerguard - which is the core of the guild. Those that aren’t part of the Hammerguard ICly often fill the rank of citizens, tavern employees, etc. That doesn’t mean the guild is OOC.
Though if you’re looking for more of a ‘clan’ or ‘warband’ type of guild, I wish you good luck as I don’t know of any that haven’t died out. There’s been numerous dwarf guilds, and most of them often times did not even manage to get started because of a lacking dwarf player base or sporadically active guild masters. Clan Stormheart is dormant again, Ironbrand Reserves disbanded, and some other dwarf guilds I’ve seen pop up once or twice are also completely inactive. There was also Of Hammers and Hollows, which I would also thoroughly recommend. Though I have not seen any of them for a long time, and as far as I know they don’t like Dark Irons so it’d be difficult either way.
If you’re looking for an active playerbase of dwarf RPers then the Hammerguard is for you. If you’d like to explore titan facilities and look for titan artifacts along with occasional RP-PvP then you might want to look into the Assemblage.
Dark Iron only RP guilds haven’t existed since Fist of Thaurissan died out, as Dark Iron dwarves either remain guildless, flock to guilds which allow any race, or joined our community.