may i use the global oe pin as the global reset pin?

Global reset is an option, that acts similar to power-on-reset, if enabled. Most HDL designs have a user defined reset in the code, it can be triggered from any pin of your choice. Unused pins should have their weak-pullup resistor enabled to avoid increased device supplied current possibly caused by floating inputs. It's a global device option, that can be set for all unused pins.