User blog comment:LilyheartsLightning/Citadel and Reckoning DLC announced/@comment-1786741-20130221185148/@comment-24174486-20130221195212

Arrival is completely optional; ME3 will reflect whether or not you did the DLC.

The same goes for ME3's DLCs. You don't need the information in the DLCs to understand what happens in the base game.