One answer would be no, this isn't allowed. 310.15 (B)(7) says it is allowable for the main feeder conductors and further states that the main feeder conductors are installed between the main disconnect and the panelboard that supplies ... Since there is no connection of the generator to the main disconnect, this isn't the main feeder, nor are these service entrance conductors.
The commentary in the handbook explains that the conductors must carry 100% of the diversified load, which these conductors will carry.
However, the last part of the section says that feeder conductors to a dwelling unit (it does not say main feeder conductors) shall not be required to be larger than their service entrance conductors. So, if this is a 100 amp service, I believe it should be allowable to use #2 Aluminum conductors.
