As I understand this is a logic level shifter not an analog amplifier - the latter would be required to get the 3.3V analog signal ramped up to 5V.
But there would be other means than just amplifying the 3.3V DAC output of a Particle device.
- PWM a 5V transistor with low pass filter
- external DAC (like MCP4725)
- use a different communication feature of the Sabertooth controler (e.g. serial)