Yes you can be asian and part of URM category. Hmong/viet and one or two other sub categories. Asians arent homogenous.I forget if it was Goro or gyngyn but one of them said schools determine who is URM.
Also one thing I remember from one school — I forget which one, I think Netter? — is that they asked what kind of Asian the applicant is and the options included Vietnamese, Hmong, and so on (korean/Chinese/japanese weren’t part of the list). So technically you can be Asian and URM at the same time? I am not perfectly sure about this