Well in the past there was some errors between Prat and nUI but as there are outside so many people using Prat, WIM and Chatmopd so that Scott make an integration for all that 3 Chatmods and they are working greatly. I using Prat myself with nUI5+. No Problems, also with the nUI_Plugin_Chat for an extra Chat on the right side.
So you really can use it. Ofcourse if you want to use an Addon try it out. If your nUI installations is gone correctly there are mostly no Problems if you see some problems with the new addon and uninstall it.
If you want to get more safe:
Safe
(Copy it somewhere outside the WoW folders) your WTF folder inside the WoW user folder or inside your WoW folder
(depends on your OS and installation place)
Install the new Addon, see what happens. Then decide to post a Bug report or uninstall the other Addon.
After the Uninstall:
Then rename the WTF Folder
(e.q. "WTF Addon Test") and copy your saved WTF folder inside the WoW folder. Then start WoW and your settings should be back. If you you do something wrong
Everything well again, can delete the renamed WTF folder.