general electrical question (with regards to the LBO pin on the Adafruit boost 500 lipo board to a Raspberry Pi)
You are correct. Although the chip’s LBO is open-drain; the LBO signal is pulled up to VBAT on-board via a BRT (bias resistor transistor).

From the schematic:


So, if you need to level convert the board’s output, follow the advice from Spehro Pefhany:


  If you want 3.3V level, you can use a PNP transistor (eg, 2N4403), emitter to +3.3, base through 3K to the LBO pin, and collector to ground through 1K. Pick the signal off from the collector.