Getting Help Without Creating More Problems

This question has a strong legal component to it that you would be wise to consult a local immigration lawyer about. The answer you might get may well vary from locale to locale. Having said that, let me briefly comment on your question.

A related question that you have not asked is about the financial side of getting help. You have not stated whether the friend's brother has health insurance to pay fro any care that they receive. Depending on how your state administers programs such as Medicaid, there may or may not be public insurance programs to be able to help your friend's brother finance hospitalization and any other treatment that is provided. However, hallucinations are a serious symptom and depending on how this is being experienced could provide for there being a threat of harm for your friend's brother or other's around them. Getting care is important.

In general, health care providers are not interested in the patient's immigration status unless this would be important in terms of exposure or ability to provide/receive care. While some jurisdictions may ask health care providers to report illegal alien status to authorities and occasionally jurisdictions may have asked health care providers to explore this with their patients, these aspects are not the norm. Generally, jurisdictions recognize that public health needs trump immigration issues. In fact, in some jurisdictions there are policies that prohibit collecting this information in order to try and protect this confidential line. In public hospitals in New York City, there are frequently undocumented illegal aliens who come to the emergency room - not only is their immigration status a non-issue but so is their real identity and ability to pay (bogus social security numbers are often entered in even when doubted). The government focus there, as in many other locations in their own way, is public health.

If your friend's brother is concerned about the hospital, you might want to suggest that that person first see a local mental health professional. While it is likely that that individual will encourage the person to go to the hospital or to a psychiatrist, it may be that simply finding this other person will make it easier for your friend's brother to accept that it is safe to go to the hospital (presuming it is). This will also provide a connection with this clinician who may be useful for post-hospital care if your friend's brother does need to be hospitalized.

You have raised an example that has the thorny issues of additional barriers to treatment as well as the cost of mental health care as a barrier. However, with a little investigation, you can find a way to move forward that will help all to find and experience peace and wholeness.