As long as the hamburger has been properly stored in the freezer then the hamburger will still be safe to eat way after the use by date.
I've kept frozen hamburger in the freezer for up to 8 months past the use by date and although it wasn't as fresh as it would've been before or on the use by date the hamburger was still very safe to use.
As long as the hamburger has been properly stored in the freezer the hamburger will continue to remain safe to eat after the use by date.