This was with me actually installing pysnmp on the omega with "pip install pysnmp", so it was trying to compile it on the omega and I'm guessing even if I did "pip install pycrpytodomex" it would have had the same results.
installing gcc, after uncommenting the base and packages lines for openwrt in /etc/opkg/distfeeds.conf, seemed to do the trick. Though, I ran into another problem. It ran out of free space, not on my sd card, but on the /tmp mount. I'm not sure how to increase that, or if I really need to, but for anybody else that might come across this the solution was to specify a build folder for pip like this.
Turns out pillow requires zlib and jpeg. You need to install zlib-dev "opkg install zlib-dev". I was unable to find jpeg. I assume there's a way to do that but I haven't ventured far enough into this to be able to try that. You can get around the jpeg requirement by disabling it in the installation arguments.
I was using a JSON file to store data from the script. I don't know why it took me so long to do this, but I included the logging for the script in cron and an error was generated indicating that it could not find my JSON. It appears when running the Python script from the shell, it must use the working directory. I included the full path in my script and it works now.
Though, I have no idea what changed from yesterday to today...
Tip of the Day: Use the logs to help diagnose an issue. They are terribly useful.