Can I boot into other OS (such as Ubuntu) from an Android OS tablet that have a USB host?
Short answer: No.
Longer answer: The thumb-drive version of Ubuntu is for x86 processors. There are ways to run Ubuntu in Android, all of them requiring a Ubuntu port with an ARM architecture. Search for Complete Linux Installer in the Play Store for basic stuff. It will rum on top of Android in a virtualized environment, and you can connect to its environment and everything. Just download the image and put it on your flash drive instead.