We're starting to develop some apps for clients and need a central place for clients to manage content. Content will then be loaded/synced to the app on startup. Has anyone used MODx for this?
No but we're planning a project to do this. But it strongly depends on what techniques you're using to build the apps. I recommend JSON.
oh ok. so is there not an ios/android api for database syncs/download?
This is not a MODX problem but a mySQL API problem. I'm not sure about Android but there are a bunch of questions on stackoverflow about how to access mySQL inside of iOS.
That's why I'd change to JSON or something similar.