The answer to this is "yes" and "sometimes".
Almost all RTMP enabled sources, including apps, will work over DaCast. The issue comes up in the login and password step. Unfortunately, most (not all) apps do not support a login and password and therefore can't be used to live stream over DaCast.
For those wanting to stream over the All Device/HTML5 channels, we recommend Broadcast Me. This is a paid app, but one that does support the login and password method and has been tested over iOS devices.
Note: most comments below are from before Broadcast Me released their latest version.