Will my ex get it vacated if he filed for child support modification & a week later filed motion to vacate divorce judgement?

It may be argued that his filing of a motion to modify the judgment acts as a waiver the the right to seek vacation of the judgment. But you have not provided enough information to answer the question as to the attempt to vacate the judgment, Dates are very important in any attempt to vacate a judgment. Unless he is arguing that the Court lacked jurisdiction, a motion to vacate filed with 30 days is a little easier than a motion to vacate filed more than 30 days after the entry of the judgment. After 30 days it becomes much more difficult to vacate a final order.