Question

I am an iPad only user and wanted to use a VSTi bagpipe (or other third party instruments) in my scores.

Answer 1

No way to drive directly that I know of. You can export a MIDI file to a DAW that is installed on your iPad (Auria Pro or Cubasis?) or a DAW on your computer and drive the VSTi that way. For the other instruments, you could solo each track one by one and export the WAV files and then import those into your DAW to make a mix.