I work with MIDI in DM1 and Cubasis in two ways; first, I might put some pattern together as a song in DM1 (that is, my drum programming is done all in DM1) and then record the MIDI from DM1 to a MIDI track in Cubasis. Second, I miss out the programming in DM1 and program straight to a Cubasis track and send the MIDI out of that track to DM1. In bot cases, I eventually route the audio from DM1 to Cubasis via Audiobus when I have my drum track pretty much where I want it.
In the first route, as the two apps are not sync'ed via MIDI, this does, of course, require you to line up the resulting MIDI track within Cubasis with the rest of your project after you have recorded it but this is easy enough to do.... I use an audio count in on a Cubasis track to help me trigger DM1 playback as close as possible - low tech but it works well enough.
I like the flexibility of having the MIDI in Cubasis. If I want to return to the drums and tweak then I can just use the MIDI editing in Cubasis and re-record the audio once I've made the edits.
I agree with Oliver though - MIDI is still a little bit wild west in iOS - although things are improving. For example, in getting MIDI in/out of Cubasis from DM1, as well as switching on MIDI note in/out to Cubasis within DM1, I find I need to set the Cubasis MIDI Connections in the MIDI track concerned to 'virtual MIDI' despite DM1 appearing as one of the options.... set it to DM1 and nothing seems to get recorded....
Being able to sync via MIDI Clock would be good though... but this is not somethings many iOS music apps seem to support as yet.... although it seems pretty well implemented in Sugar Bytes Thesys step sequencer app....
Hope this helps?