Data is a technological device, and thus can be assimilated. It would be no different than the Borg subverting a ship's computer systems.
Whether or not Data can *fight back* is unclear. But the Borg can certainly try.
I also recall hearing more than a few times that the Borg needed their organic parts in order to survive.
That applies to drones which had organic parts in the first place
, yes. But we've seen Borg taking over computer systems, and Data would be the same. You don't need organic parts to survive if you never had them. The Borg are a collection of millions of different species; some of these surely were not organic.