My question is this is the mantra Om Ah Hum Benza Guru Padma Siddhi Hum a Vajrayana mantra? Can I chant it? I am asking because, I’m wondering why I’ve had the company of hallucinations? Will the mental health problems be permanent, until I see a Lama to give me my refuge vows?
If reciting a mantra is causing you to hallucinate, I would recommend immediately stopping that practice.
Formal refuge under a Vajrayāna guru cannot cure mental illness. It can't even cure depression. The Buddhadharma isn't about making one's life more comfortable (not claiming you said so).
I don't know anything in-depth about the Vajraguru mantra (that is the name of the mantra you inquired about). Because it is Guru Padmasaṃbhava's mantra, you chanting it without initiation is likely a mishandling of the mantra according to the traditions that use that mantra.