Yes, you can backtest, optimise and apply the EAs* of your choice on both MT4 and JForex.

As JForex is a Java based platform, EAs applied to JForex accounts need to be in Java programing language.

Choosing, evaluating, using and monitoring an EA is entirely at client’s own discretion and should not be in violation of Tier1FXTrading Rules and Regulations
For more details on Tier1FX EA Policy, please read here