Now that I've got this setup working, I am seeing a few possible issues - but have not yet been able to rule out user/software errors. iPad 2, iOS v. 8.3.
I've tried a few iPad apps including "Thor" and "Modular" synths, and "DM1" drum machine and I think I am having issues with MIDI channel crosstalk? All those apps are able to listen to all/omni or individual MIDI channels, and are compatible with Audiobus. I have sequencers 1 and 2 on MIDI channels 1 and 2 and the drum sequencer on channel 10, and each app is listening to an individual MIDI channel.
In some situations I am finding if I have notes play on the same step on more than 1 channel, the other channel fails to play anything for that step, unless I mute the other sequencer(s). I'd like to explain my issue clearer but I am still learning how to use MIDI to begin with.