FME Cloud (or FME flow hosted) runs on ubuntu, so you would have to install it on that machine. The command for installing tessaract on ubuntu is: sudo apt install tesseract-ocr

There are many caveats for installing this software in the cloud. firstly it installs natively on the processing pod, this machine is just a temporary machine, and does not support mutating installations over a longer period of time, since it can be swapped.

You have permantantly storage in your resource folder, if you were able to install it there I believe you should be able to run it safely. But then you must remember to call the full path of the binary since it not in any system directory.