Relationship with non-US resident on temporary visa? good or bad?

I need your opinion. My brother is involved with a woman from the Dominican Republic. She has been in the US since 2005, on and off. She claims to have a 10 year visa, she has to leave every 6 months and go to her country per the visa. The visa's 10 year expiration is expiring in 2012. This woman does not speak english, has no skills whatsoever, no family here, only a sister that she is not on good terms with, and she is involved with my brother, who has no idea if she is legal. I cannot even communicate with the woman, as she does not speak english...I have no idea how my brother communicates with her....I am worried. My brother is in a rut, his job is not secure, he is not a motivated type of person, and afraid of being alone when he turns 50 yrs old soon. He claims no one will want him when he is 50 yrs old. He is considering marrying this woman with a pre-nup. He never met her family, and never has been to her apartment. She claims that she rents a room and landlord forbids guests. He says that he is sick and tired of the dating scene and cannot start dating again. He will settle for less. If this were your brother, would this relationship raise a red flag in your eyes?