a) If the physical hardware is dedicated to the end-customer, then YES.

b) Office 365 ProPlus could also run in a shared hardware (multi-tenanted) environment PROVIDED you are a QMTH partner. Click here for more info.

c) If you are not a QMTH partner and wish to run Microsoft Office components in a shared hardware environment, you are required to procure it via the Microsoft SPLA (Service Provider License Agreement) monthly program.