usb otg thermal printer interface to android tab with usb device
Did you try this App?  Supports Ethernet, USB or Serial (with serial-USB adapter). 
https://play.google.com/store/apps/details?id=qsrtech.posprintdriver

Also, try this app from Opera Mobile Store. If this app doesn't work with your printer, send printer profile to the app server. They might add support.
http://apps.opera.com/en_in/usb_printer_driver_21_developer_edition.html