It doesn't seem right that they would let you book a connection under MCT.
​​It wouldn't surprise me if you did book the short connection that they will then rebook you on the later flight
If it's me i just wouldn't book that even with same ticket protection, if something goes wrong you may not get rebooked on the next flight.
The chance of getting a jet bridge directly into the terminal is slim at SGN, so most likely a bus gate.
I always err on the side of caution in Vietnam.