Yes. But syncing means different things to different people, so –
If by syncing you mean automatic syncing of changes–that is, your changes sync from device to device without you having to do anything other than giving them time to sync–then you must use Dropbox, as it’s the only supported automatic syncing service for iOS Scriv.
However, if you’re okay with you transferring copies of your entire project from device to device via a syncing service, then there are a few alternatives to Dropbox discussed in this thread.
You may also be interested in looking through the articles in the iOS Scriv Knowledge Base, as well as the Cloud Syncing Knowledge Base .
Best,