It definately needs to be sanded if you are shooting for a thourough and quality job. To many replacement panels have runs and paint flaws that you don't want showing up after you have painted it. And almost every one I've worked on needed some straightening by block and hammer or skim putty. Just a warning, these reprodution facilities tend to make parts in batches and I have found several that had light surface rust under thier primer from when the steel sat either prior to forming or prior to priming. I found this by prep sanding it with some 200 grit, next thing you know the black primer is popping off in places with rust underneath.
Sand it and keep your eye open for bubbles and runs.