Solved it. Turns out in your ParagraphStyle it needs to be fontName="Arial" not font="Arial" but I did learn some other tricks of getting it to work in other ways below.
styles.add(ParagraphStyle(name='Address', fontName='Arial')
After doing some digging I've learned a few things that I hope helps someone else in this situation. When you add the tags inside of your Paragraph around the Unicode text and set it explicitly to a font it will work.
elements.append(Paragraph(u'<font name="Arial">6905\u897f\u963f\u79d1\u8857\uff0c\u5927\u53a6\uff03\u5927</font>', styles['Address']))
This fixes the problem at least for Paragraphs with various fonts. Again this code will work.