Creating parts of terrain with different tools

I never created terrain or vegetation. Can someone explain one thing? To create terrain with simple trees and grass I can use some free tools. I choose one for terrain and another one for some better vegetation.

So is there any compatibility thing between tools? I mean, if I start with one tool, will some other tool be able to put grass correctly on the terrain surface?

Asking because I understand that if I do it using one single tool, it knows what it does and can add vegetation correctly. But what if tools are different for different parts? What is the workflow? I should know how to approach before I start.

If I get you perfectly, you intend to create a terrain with grasses? The tools are well separated in unity. Click on your terrain and check through the settings. If you run into further problems, let us know.