The art of Synthesizer design involves using several noisy sources, in various ways, to achieve the good end-result you want.
Yes a pll will amplify the spurs of the DDS by 20 Log N, but ONLY inside of the pll control loop bandwidth. If you have a 1 KHz loop bandwidth, and you have a spur at 1 MHz from the carrier, it will be amplified by 20LogN, but reduced by maybe 60 to 100 dB in the loop filter's lowpass response! So the answer to your question is "maybe".
Mixing the DDS with the VCO, and then presenting it to the digital divider eliminates the 20Log N DDS spur amplification, but adds parts/complexity, as you do not want to lock up to the image frequency out of the mixer! May require pretuning the VCO with a DAC, or maybe a image reject mixer, since the DDS you are thinking about is low frequency.