Teensyduino only supports the Arduino IDE files published by Arduino.cc. Copies modified & packaged by distros are *not* supported. If you have a copy of Arduino that can from Ubuntu (which is likely an ancient version, not to mention Ubuntu's changes), the installer will not recognize it. Only the copies published by Arduino.cc work.
Currently Arduino.cc publishes 3 versions for Linux, 32 bit X64, 64 bit X86 and 32 bit ARM. They don't publish a 64 bit ARM version. If they ever do, I will publish a 64 bit ARM version of Teensyduino to support it. But until that day, there simply isn't any support for 64 bit ARM.
If you *really* want to try to create one, it may be possible. But if you can't get 32 bit libs installed on your machine, it's probably not worthwhile to try. If you can run native 32 bit programs, you might be able to cobble together a working Arduino 1.8.5 IDE by just replacing its JRE with a 64 bit version. Or maybe you can delete its JDE and using classpath or editing the arduino start script coax it to use your system's JRE. But beware, things are almost certain to not work if you have a non-Oracle JRE, or a version that's too old. Arduino 1.8.5 uses Java version 8u144, so make sure you get that version if you use Oracle's website.
Once you get a working Arduino IDE, then you'll need to do all the stuff the installer does. The hard part is pde.jar and arduino-core.jar. You're going to need to build these with the Java JDK and ant (hopefully Ubuntu provides a working "ant"). The source code is here:
https://github.com/PaulStoffregen/Arduino-1.8.5-Teensyduino
To get the rest, you should be able to just run the 32 bit ARM installer on Raspberry Pi. Then copy the contents of hardware/teensy and hardware/tools into your custom built copy of Arduino. A bunch of the stuff in hardware/tools will be 32 bit ARM, so again you may need to mess with installing 32 bit versions of libraries they use.