Q:

Appreciate if someone can clarify the following on the TPS65820 PMU. 
WLED supports only single chain Series LED, However, I would need two i.e. LCD and Keypad Backlight. I am looking for proposal for the WLED to drive both the LCD Backlight and Keypad Backlight. Can I use the Open-Drain LED_PWM to sink the Keypad LED backlight driven from the WLED boosted voltage, possibly with a small series resistor to limit the max current?

A: 

I don't see any reason why you can't use the open-drain PWM outputs to sink the LED current as long as you don't exceed the Vol spec of 150mA.