I think it can do Dropbox but advises against it, not sure if thats a speed thing or a structural thing, have never lost a file with the iCloud sync but frequently seen all sorts of randomly named files from using other apps with Dropbox. Hoping soon everything will work nicely with a SCriv on all my devices/computers 
Well, that’s not my experience with the iPad/Phone versions of Ulysses - with Editorial and 1Writer, for example, you can browse Dropbox and read and write to useful folders like nVA notes, or Scriv Sync or Scriv Scratchpad, but Ulysses just says No (except for the Mac version).
Never had an issue myself with lost or odd Dropbox files (and I use it as an organisational hub) but the point is that iCloud doesn’t give access to any of the folders I’ve mentioned. Nor will it, I presume, when iOS Scrivener arrives, which - happily - seems to be fully Dropbox ready.
It took 10 seconds for writing in the phone app to appear on screen on the iPad, didn’t need to press sync or anything. I will love it if we can do similar with Dropbox, in my experience with all the things that claim to be able to sync to Scrivener that has not been the case, and there are lots of posts on here from people complaining about third party apps (I’ve tried just about all of them and they’re fine until you want to sync).
Allow me to vent, now that I have been directed to the “proper” forum. AHEM.
I’ve cobbled together a method, where, when I want to get away from the desk and laptop (usually by Noon), I’ll pick up an iPad and a bluetooth keyboard, open Ulysses III, and have a go. Save the work, or hope (at least) that the autosave feature really does auto save, and close down for the day. Next morning, open Scrivener and Ulysses III again, cut/drop/paste yesterdays text into a sheet and store in the proper file. That allows for later editing. If I don’t watch the cut/drop/paste, I will have bits and pieces of my latest work scattered all over the place. Not comforting, but workable.
So, please. Get the iOS for Scrivener working. Ulysses III is fine, and worth the $$, but it isn’t Scrivener for editing chunks of work or planning/outlining. I need continuity in the software, where I’m not having to hopscotch from one to another platform. It becomes tedious.
When is Apple supposed to be done with the review? Any more teasers?
The Bard
Editorial, is a great markdown app as well.
Ulysses mobile (Universal iOS) will have Dropbox support via external folders, but the latest beta also allows for an alternate Library database. Normally the library is through iCloud, but now you can add a library through Dropbox. That’s two separate databases that you can copy/move sheets to and from. Another thing is, you can also set up multiple Dropbox accounts, one through the Dropbox app allows, and another through the Web allows. But once they are set up, you no longer need to open Dropbox, just select 1 of the 3 libraries inside Ulysses.
However, I can’t remember if these features are currently available or will be available in 2.6.
I’ve found I like the workflow, on iPad or iPod Touch, to work in Scrivener iOS, then export my novel or blog posts to Ulysses mobile, then pretty-fy it inside Ulysses, and then either export to epub in Ulysses Mobile or post to medium sized r WordPress via Ulysses Mobile. But that’s only IF working solely on an iDevice.
If working on desktops and mobile, the desktops of either Ulysses or Scrivener have more robust features. Both are great apps, they just have differing views on how to store and getting export your written works. Try the trials, figure out where ch works best for you. In my case, they both are great for my workflow.