I do not think Pakistan Military will opt to have data links routed through private or western firms. IMO either Chinese (again doubtful) or Pakistani built satellites (most likely) will be used for this purpose.Yes , all the systems you mentioned must have a satellite navigation system?
Beidou has a text messaging system for paid users / military users.
I would like to know if Pakistan being a partner in the program and having access to encrypted signals, makes use of this facility?
The missile can send back a text message, with last position data, before impact. That will confirm a hit or a miss.
Though we have not seen REK being used to carry tactical nuclear warheads, but possibility cannot be ruled out. However, Ra'ad can carry nuclear warheads. Such systems cannot be risked to have comm link routed through foreign satellite channels.