I know of none of my atheist friends who celebrate Easter with bunnies and eggs and know of no Christians who don't except maybe the JW's, but for the sake of argument I will concede that if they do then yes, they are also
co-opting a pagan holiday.
I'm not Christian anymore, but I celebrate it as a family day, because you know, quite frankly, we need at least one of those each year (and besides, whatever name it has, it was
co-opted by Christians from a much older,
pagan holiday, so it's fair game).