The APU does not monitor ac or dc pump for starting purposes. The APU SOV is motor operated does not require fuel pressure to open. It opens when the APU start switch is selected to ON.
The APU DC pump only runs if the Fuel System press sw says low press. There is no need to pull the DC pump C/B. (The APU dc pump press sw. only turns on a fault msg).
When the APU is first started, the DC pump will run. When AC power is supplied, the right boost pump will take over. The Fuel System pressure switch will shutoff the DC pump.
If the AC power is already being supplied, and the right boost pump is on and supplying pressure, the DC pump will not run.
I can't be sure of this but if the APU is started and the AC and DC pumps do not operate, the APU fuel pump may be able to suction enough fuel to start.