You’d have to make sure the engineer has Omnisphere, and the same settings you are using within that, to get it to sound the same. As Martin indicated, MIDI is just data for attributes such as notes, controllers, etc. There is no sound in that data. The sound comes from whatever instrument the MIDI is driving.
Depending on why the engineer wants the MIDI data (e.g. maybe he wants to bolster the sound from some track within it with some other virtual instrument or a hardware instrument), you may need to provide both the MIDI and the audio if it is important to have the same sounds from your project.
If you export the file as a “MIDI loop” it will save the file along with the instrument and patch, however my guess is that it will probably only work in Cubase