Honey is said to be the only natural food product that doesn't spoil. According to accounts from the time Alexander the Great's body was packed in honey when he died to preserve it for the long ,hot journey home.I don't know you can say Freezing is = to sanitation. Freezing yeast to normal freezer temps doesn't kill it, why would wild yeast die off? I would think you really want to avoid Lacto, Pedio, and Brett in your melomel, but I don't know maybe you do? If you want to avoid them I am pretty sure Freezing for <24 hours wont do the trick. Plus these berries have been through a lot to reach that shelf you bought them off of, who knows what dirt, from what surface got kicked up or came into direct contact to those berries...From what I understand, honey has some natural antimicrobial properties in addition to the low pH and alcohol content of a finished mead. I've heard several reports of people intentionally trying to make a sour mead and being unsuccessful, so I have little concern with unintentional contamination.
Personally, I've never sanitized fruit in any melomel (primary or secondary) and have never run into any contamination issues.
I made mead before beer and had to learn the hard way when I started brewing beer to take sanitation seriously. My girlfriend had been making mead for years before that and had come to learn that infections just didn't happen and would, for instance, give the bottle bucket and autosiphon a quick rinse with tap water before use. Now I apply the sanitation I find necessary for beer to mead just out of habit.
My understanding of honey's ability to stop anything from growing is only in its pure form. The sugars are so condensed that the cell walls of any normal yeasts or bacteria are broken by the pressure thereby killing anything that gets in the storage container. This won't be as true once you dilute the honey. If the yeast can survive to ferment it, the bugs can survive to infect it, prior to completing fermentation. As has been said once the PH drops and there is alcohol present you should be okay adding fruit, hops, coffee, spices, nuts or whatever.