Are there any clinical trials using radiation therapy for hiv?

I don't think so. Radiation is more standardly used to treat cancer and not illness such as hiv. Radiation has been used to treat kaposi's sarcoma which can be seen in HIV patients. Hiv medications are also being tested in combination with radiation to see if they make radiation treatment more effective. Also, radiation is a local treatment and HIV is a systemic problem so it doesn't make much sense to use.
No. Success has been achieved with medications and hopefully one day with a vaccine. Radiation will not have a role in treating HIV unless it's the cancers those patients are prone to.
Not directly. Viral particles are one of the most radioresistant organisms around. As pointed out, HIV is a systemic infection affecting all the body and radiation will cause more damage to the host than the virus. However, radiation can be use to treat HIV related disease such as anal cancer, head and neck cancer and kaposi's sarcoma.