All versions of Caddie from Version 15
Yes you can. Copy the .pat files into the hatch folder and Caddie will use them. To find out where the hatch folder is located, open Caddie then go to
MENU->SETTINGS ->ENVIRONMENT SETTINGS
and expand the Folders option.
Alternatively (if using the default folders) go to
MENU->UTILITIES->BROWSE->COMMON APPLICATION FOLDER
This will open Windows explorer. There you will see a folder named "HATCH". It is in this folder where the Custom Hatch patterns (*.PAT) are stored. Caddie will automatically pick these up when required.