PWM photodiode bias circuit control voltage
Well, a PWM pin through an RC circuit basically acts like a DAC, so as long as you use a low enough cutoff frequency you should be fine.  That being said, the circuit you linked probably needs an external RC filter for the control voltage input.  It looks like C8 and C9 are required to reduce output noise by slowing down the response of the converter by limiting the feedback bandwidth.  However, feeding a signal with lots of high frequency components (e.g. a PWM signal) directly into the feedback pin will cause issues.  So, as long as you add a decent series R and a nice big C right on the Vprogram side of R4, it will probably work just fine.