A Factory Reset is not in any way a highly processor intensive function so a 30% charge on the battery isn't an issue. Factory Reset does just one thing, it wipes the user data partition clean and that's it. It doesn't affect any of the system partitions, it doesn't magically do anything to the installed Android operating system, it just clears the data off of one partition in the internal storage media.
But you would be better off waiting a bit to charge up your device more. The Reset itself isn't an issue, it's the reason as to why you're actually needing to do a Factory Reset that could be something to consider. If it's stuck in a boot loop, a Factory Reset 'might' solve the issue but keep in mind that you'll also be wiping any saved data and personal files. Hopefully it's a matter where you don't have anything vital stored on this tablet or that you have backups.