Yes, the cellose will "in TIME" settle, but I don't know that time frame.
I blew in cellose in a home one year and returned the next to install some bathroom exhaust fans and the cellose had not settled at all.
Cellose does have a tendency to bunch up and dam up at the end of the run. Ideally, cellose should be showered down like rain does on a windless day. But in the attic the cellose does bunch up on the high sides and the lee sides are bare.
I usually get a broom and correct this by hand after blowing, however, you will not have this luxury.
JUst thinking out loud, could you not lay batting down and push it in place to create your vent system and to lay it down properly?