Does Gelato Freeze?
Of course it can.
Whether gelato will freeze "as hard" as an ice cream sandwich (whatever you mean by "ice cream sandwich") has less to do with the amount of butterfat in gelato vis-a-vis ice cream, and more to do with the amount of sugar, as well as the alcohol content of the mixture.
Too much sugar in a gelato or ice cream mixture will mean it won't freeze properly (sugar lowers the freezing temperature), while too much alcohol in a gelato or ice cream recipe will prevent ice crystals from forming.
So how "hard" something will freeze depends not on the labels "gelato" or "ice cream sandwich" but more on the amount of sugar and/or alcohol in their ingredient mixture.