Random thoughts:

If you're planning a sealed CO2 setup, disregard my rambling.

1. The diagram shows a sealed air line from one end to the other, which prevents the flow from being used to circulate air in the cabinet (assuming this is a cabinet plan). If you leave the first tube's intake 'open' and take the hose off the main intake, the fans will give the plants a constant fresh breeze, moreso if you switch the main intake to the other wall.

2. It might be better to make separate exhaust lines leading from each hood and link them at the wall with a Y-adapter. That way one of the bulbs won't be washed in pre-heated air from the other. Fan #1 would either need to be larger than the other two or replaced by a large passive intake and reassigned to ventilation duty in the veg room.