I'm pretty sure they are sandboxed and can't access the network at all. Actually looks like you can set a flag to access the network.
https://developer.apple.com/library/ios/documentation/Genera...
https://developer.apple.com/library/ios/documentation/Genera...
Big scary warning, I like it. Swiftkey does badger people to enable it though, so presumably it's sending a lot of data back to their servers as a business model. Nasty.
https://iossupport.swiftkey.com/hc/en-us/articles/201466641-...
I think Nasty is a bit strong here.