As noted in the lore thread just below this one, so far we know that Midlander, Highlander, Lalafell, and Au Ra, do or have called themselves Doman. Looking at the third race there, the Lalafell, one could probably assume that any major hub city, particularly a port city, has been inhabited by most or all races. How deep seated they are in the culture, I am not sure, and can't be until we either go there, or get more information, I would say that there are citizens of Doma who are Miqo'te, and that they have been there for long enough to call themselves part of the City-State.
Now, I think you said outside of Doma in the mountains? As if they had traveled over land bridges to get to Othard as a clan? I think that would be a little harder to justify. There would be little to no reason for even a nomadic tribe to travel that far to settle without the use of the sea routes, which have been around for some time now. If it were the case that a nomadic tribe needed to move, that is a far distance, and even Auri tribes who are nomadic by nature don't seem to have moved that far out of their way. (This is not to say, that it has never happened, just that it would be harder to assume!)
My suggestion? Move a small band by sea or by landbridge, and not a full tribe, or multiple tribes. Or, have them taking sea routes to Doma, only to find it inhospitable for whatever reason, possibly because they felt the encroaching threat of the Garleans even before the empire razed the city, and left to avoid it after having settled in the city. These two seem more likely, but also shorten your group's time in the mountains, and so would make it harder to call them a mountain dwelling tribe by way nomadism and then tradition, but rather a mountain dwelling tribe out of necessity.
Hope this doesn't crush all your dreams, and helps you find a good backstory instead! Good luck!
Now, I think you said outside of Doma in the mountains? As if they had traveled over land bridges to get to Othard as a clan? I think that would be a little harder to justify. There would be little to no reason for even a nomadic tribe to travel that far to settle without the use of the sea routes, which have been around for some time now. If it were the case that a nomadic tribe needed to move, that is a far distance, and even Auri tribes who are nomadic by nature don't seem to have moved that far out of their way. (This is not to say, that it has never happened, just that it would be harder to assume!)
My suggestion? Move a small band by sea or by landbridge, and not a full tribe, or multiple tribes. Or, have them taking sea routes to Doma, only to find it inhospitable for whatever reason, possibly because they felt the encroaching threat of the Garleans even before the empire razed the city, and left to avoid it after having settled in the city. These two seem more likely, but also shorten your group's time in the mountains, and so would make it harder to call them a mountain dwelling tribe by way nomadism and then tradition, but rather a mountain dwelling tribe out of necessity.
Hope this doesn't crush all your dreams, and helps you find a good backstory instead! Good luck!