Is it safe to only use a Smart Cover case for my iPad?

If you take care of things and aren't the type of user who drops expensive electronic devices, sure they're safe for normal use. Millions of people do use them. If however, you are prone to dropping things, a more secure iPad case offering more protection might not be a bad thing to consider. These devices cost a LOT. iPad warranty does not cover drops. So think about your needs and choose accordingly.

With such an expensive device, I wouldn't risk it.

Get a good protective case for that iPad Pro.

Don't take any risks.

If you haven’t purchase two-year extended AppleCare+, an accidental drop and breakage will cost you a lot to repair/replace that expensive iPad Pro as the free, standard, one-year warranty does NOT cover drops or other types of accidental damages caused by the user.

Best of Luck to You!

As long as you are careful it should be fine.

I've used just a Smart Cover for my 12.9" iPad Pro for the last 3 years, and its fine.