Is it possible to provide DAC voltage to VOUT_ADJ to control Vout?
Yes, this is certainly possible.

FB stands for "feedback", and the feedback voltage is 1.2V according to datasheet. So, in normal operation Rup and Rdown resistor divider is used to bring desired output voltage to 1.2V level, no Radj necessary.

However you can apply external control voltage via Radj to shift the equilibrium point up or down. The proportion between three resistors plus the output range of your DAC will define the effective adjustment range.

I did not read datasheet in detail, but I suspect the efficiency of the conversion will suffer if you move output voltage too far from the design point. This feature is not implemented to build something like adjustable bench supply, but rather to fine tune the output (add temperature compensation, for example).