No, raider attacks can not occur while you do not have the app in the foreground.

No incidents occur while the app is closed. Only two things can happen while in the background:

1. Resources will continue to be consumed for a short while after moving to the background
2. Timers for production, child birth, and S.P.E.C.I.A.L. leveling will run to completion.

No, raider attacks can not occur while you do not have the app in the foreground.

No incidents occur while the app is closed. Only three things can happen while in the background:

1. Resources will continue to be consumed for a short while after moving to the background
2. Timers for production, child birth, and S.P.E.C.I.A.L. leveling will run to completion.
3. Wasteland explorers keep on exploring (and looting and getting damage).