Yes - we do already have basic MIDI record/play-back functionality within Hauptwerk logged as an enhancement request.
I have Logic Pro as a sequencer for the Mac, but Apple also make a cut-down version: Logic Express:
http://www.apple.com/logicexpress/
I haven't tried that, but perhaps that's worth having a look at, if you haven't already done so. It has audio sequencing capability, but you could just ignore that.