Let me answer these questions for you:
1) Yes, ownCloud starts to sync documents edited offline as soon as you hit a network again. For example, with the desktop client, files are changed and synced as soon as the desktop hits a network connection and can see the server (windows, mac, linux). On iOS devices, they are queued and again, as soon as a user comes back online ownCloud will upload the files.
2) ownCloud uses the standard ownCloud registration mechanism for opening and editing files, and as long as this is supported in the app, owncloud can use it. Right now, that includes the apple suite of products, as well as:
- Olive Office 2 ½ stars
- Documents 2 4 stars
- CloudOn 4 stars
- Paperport Notes 3 stars
- AstralPad 3 ½ stars
Any other questions, let me know!