OmniFocus 2.16 for iOS is now in TestFlight, with support for using specific folders or projects as targets for /paste URL actions. Enjoy!
Yes, I totally agree: right now, the iOS app only supports automating the “Create” part of the traditional set of database operations (unlike the Mac’s support for AppleScript, which can Create, Read, Update, and Delete). We want to flesh that out completely eventually, but it’s not at the top of our roadmap yet. (There’s only so much harm someone can do with Create, but we might want a stronger security model in place before allowing those other operations.)
The separator is actually a synced database setting that used to be controlled by a visible preference in OmniFocus 1. Is it possible you customized it in your database at some point?
Have you tried copying a task which has the nested context assigned to see what it looks like on your device? You can do this by editing the task, using Share > Copy, then pasting the text into a plain text context (such as a note in OmniFocus, or a text editor in another app).