I'm not familiar with the Harmony One. If the software it uses allows the entry of pronto codes than yes you can. If it is like the Harmony 900 which uses a web based utility exclusively, you will need to teach your Harmony One from another programmed remote.
I have a USB-UIRT, which is an IR remote send and receive unit. I entered the pronto code into IRTool (software for IR) and had my Harmony 900 learn the code from it.