Yes Drano Max Gel is very safe for septic systems and I've used it myself several times when I had a septic system and it never harmed the septic system and was very effective at cleaning and clearing clogs in drains.
You can also use vinegar and baking soda mixed together in a drain to clear a drain more naturally which is also a safe natural drain cleaner for septic systems.
Just pour some baking soda into the drain and then pour some vinegar into the drain after the baking soda and the baking soda and vinegar will react together to clear the drain.
Just cover the drain with a drain plug or rag to allow the vinegar and baking soda to work together in the drain.
Then pour some boiling hot water down the drain and eventually it should unclog the drain as it's worked great for me.