Should I use a dehumidifier for my piano room?

No, no no no, and no.

A piano will absorb moisture from the air. When the humidity is high, the piano absorbs this moisture, and this affects the tuning. When the humidity in the air drops, the moisture leaves the piano.

A dehumidifier in the room will remove moisture from the air. Great. The moisture in the piano might drop. However, the dehumidifier turns itself off when it is too full. Or sometimes, people turn it off before going on holidays.
Once it is off, it doesnt take long before the humidity in the room is back where it was, and the piano absorbs the moisture from the air again. This can cause sharp changes from high humidity, to low, and back to high again.
In some pianos I have seen, a dehumidifier in the room can cause issues for your piano. Your piano really needs a stable environment.

If your piano is having an issue with high humidity, a solution is to install a specialty system in the piano called a piano life-saver.
This is will burn off excess moisture inside the piano, it uses a fraction of the power that a room de-humidifier will use.