How to root launch a regular Mac application from a cron job in /etc/crontab

Cron is not in any way deprecated, but LaunchD has more versatility and is used, and actively maintained/supported by Apple. Their best practices guide is here

LaunchDaemon jobs(versus LaunchAgents, which take on a users id) run in root's context without needing to enable the root user. All that is required is a properly formed XML file(you can just copy-paste pre-existing ones in /Library/LaunchDaemons, substituting your script for the ProgramArguments with the applicable schedule keys) with the proper ownership/permissions. An older writeup can be found here: afp548's launchd-in-depth article

Run a shell command that starts the other commands:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
  <key>Label</key>
  <string>some.label</string>
  <key>ProgramArguments</key>
  <array>
    <string>bash</string>
    <string>-c</string>
    <string>python first_script.py;python second_script.py</string>
  </array>
  <key>RunAtLoad</key>
  <true/>
</dict>
</plist>

Or change the ProgramArguments key to

<key>Program</key>
<string>/path/to/script</string>

and use a script like this:

#!/bin/bash

output=$(python first_script.py 2>&1)
if [[ $? = 0 ]]; then
  python second_script.py --result true
else
  python second_script.py --result --false --reason "$output"
fi