It 100% depends on the number of cubes used to blend the frozen marg, versus the number of cubes used to put the drink on the rocks. It also depends on the method of preparation.

A standard marg glass has a volume of 9 fluid ounces, and a 1 inch cube of ice has a volume of ~.55 fluid ounces of water. So assuming you use five cubes for a drink on the rocks, your drink is about 30% water before you even add your liquor. (Though to be clear, this isn’t likely to reflect reality, as bars tend to use commercial ice makers that create hollow ice cubes.) So as long as your frozen marg is less than 30% slush by volume, the frozen marg will be stronger. And the exact liquor:slush ratio really just depends on how thick you like your frozen drink; More ice means a stiffer/more frozen drink.

If the frozen marg is made using a commercial frozen marg machine, the frozen marg will almost certainly be stronger; The marg machine doesn’t actually add any ice to the drink; It just freezes the water that is already present in the liquor and mixers. To be clear, the mixers (like pre-made marg mix) have a lot of water in them. But conceivably the frozen drink would be using that same mixer too, so there shouldn’t be any difference in the actual liquid ABV. No extra water being added to produce the ice means the resulting drink is stronger. But the refrigeration required for that doesn’t efficiently scale to smaller sizes, so at-home machines usually require adding ice to the mixture and then blending to break the ice into slush.