I have a website which uses a socket to connect to MySQL. The format for this in DB_HOST looks a bit like 'localhost:\tmp\mysql5.sock'. Your plugin currently does not support sockets since it does not use WPDB.
I made a very small update to two files that call mysqli_connect to fix this. Note that this fix does not encompass mysql_connect. I don't know if you have a git repository that I can submit a pull request for, so instead I pasted the modified functions on pastebin. Links below: