Hell yea I would shoot it if it seemed like everything was in good working order.
If he kept it cleaned and oiled, it will probably work like a well oiled machine. I would probably take it apart before shooting just to make sure its clean and to familiarize yourself with the firearm.
I wouldn't be afraid to take it apart as it looks like an easy process.
This is the k98k action taken apart
It is such a mechanically simple firearm that there is not a whole lot that can go wrong with it as long as it is taken care of and it seems like your grandpa took care of it from what you are saying.
Continue to show it similar attention (attention includes seeing some more use) and it will probably be something that you can give to your kids or grand kids.