I wonder if you ever found a way to enter Unicode characters directly on the ipad?
It's 2017.09 and the closest I've found is the app Unichar. Can't enter (uni)codes directly, but it has 18 unicode pages avaible (in the paid version, 8 in the free version.) Interesting is that it installs as an app that you can open, but also has a keyboard with the same level of features as the app and similar interface
This is as close of an answer as I've found to the same question. It's odd apple resists users' interest for so long.