Are Macbook Pros with a rusted / corroded MagSafe port safe to operate?
The iron / ferric portions of the MagSafe port is something that will corrode when exposed to oxygen. The quality of your pictures is excellent and all are operationally normal and safe since the 5 central pins are clear, not corroded and not obstructed. 

You do have a pretty severe amount of corrosion, so that might implicate the environment having salts and high humidity. If so, the insides are also likely to corrode, but not simply because the outside is rusted.

The corroded portions are not part of the electrical charge / ground / function and only cosmetic so unless your 5 pins are stuck with debris and don't have spring pressure or the corrosion / lifting of the plastic shield prevent good contact, I would ignore that entirely.

You could place a new adhesive shim or consider painting (very carefully) the area since a thin layer of paint won't affect the magnetic pull or the function unless / until that paint is a physical barrier at one of the corners or covers the pins and springs.

Replacing that part might be $30 if you buy new service parts and much cheaper if you can get that part used from Mac that has other issues (broken screen, liquid damage not to the charge board.