Does 30w adapter charging harm ipad pro 9.7 battery?

It doesn't matter which Apple power/charging adapter you use.

All iOS devices that can fast charge will take as much power from the Apple power adapter, as needed.

Some iPad users use their 59W/60W MacBook Pro power adapter!

The 30W Apple power adapter WILL NOT harm your iPad's internal, rechargeable, Lithium-ion battery.

Your iPad's battery will be just fine.

No.

The iPad will take whatever wattage it needs for charging.

It will not use the full 29/30W power of the power/charging adapter.

Your iPad Pro battery will be fine.

sorry about that 30W USB‑C Power Adapter - Apple

Check here for compatibility with your iPad pro.