I would never recommend adding anything to an axolotls tank that is unnecessary.
Your tank can be easily cleaned of algae with the algae scraper/mitt/magnates of your choice.
I did a google search on simazine and found enough to not feel comfortable with using it in aquariums:
Simazine is currently classified by the EPA as a General Use Pesticide.
What are the Health Effects?
Short-term: EPA has found simazine to potentially cause the following health effects when people are exposed to it at levels above the MCL for relatively short periods of time: weight loss, changes in blood.
Long-term: Simazine has the potential to cause the following effects from a lifetime exposure at levels above the MCL: tremors; damage to testes, kidneys, liver and thyroid; gene mutations; cancer.