Is it possible to drive a low voltage (7V) brushed DC motor with a low duty cycle, 220V DC source?
As you can see from the comments, 220 volts is too high for any serious consideration. That voltage is almost certain to arc over the commutator and likely also arc to the motor housing. It may also break down the winding insulation causing a turn-to-turn short or winding-to-frame short.

The 7-volt motor rating is the rated average voltage that would result in the rated motor speed. Exceeding the rated average voltage would result in exceeding the rated speed. That may be permissible to some extent. A 5 or 10 percent over-voltage tolerance is generally expected for most electrical products. A small brushed DC motor might tolerate 50 percent over-voltage, but bearing and commutator wear rates would be increased.

For typical PWM control, you might expect the peak voltage to be as much as 50% above the average voltage. Peak voltage that is twice the average voltage would probably be ok. Controlling the speed of the motor by changing the average voltage over a small percentage of the supply voltage is generally not a very attractive strategy even if the motor will withstand the peak voltage.

For a 7-volt motor, something like a 12 to 15 volt power supply would probably be a good choice for PWM control. Anything more than 50 volts would probably be asking for trouble.