I can highly recommend StepPolyArp and I use it all the time with Cubasis. I am using them both on an IPad Air128.
To get around the inherent Midi clock sync problems I use Midibridge as a local host and just connect SPA to Cubasis.
You can even use SPA through Audiobus to control an IAA app in Cubasis.Again StepPolyArp goes way beyond being a simple arpeggiator and the Dev is very helpful and responsive. Definitely a 5 star app!