In a perfect world I would use quality flash frozen raspberries, an extended thaw time and do other prep prior to adding them to the cake. The leavening agent in cakes relies on the heat so I would want everything pretty much the same temperature. There are exceptions to the rule like if I'm going to add coffee to a box cake instead of water. I want that coffee to be hot because that will bloom the cocoa but this isn't a boxed cake. And we're not adding coffee. I would place him in a single layer in between some paper towels. That's going to leach out excess moisture and keep the baking ratios where they need to be. Lastly I would toss the raspberries lightly in some 00 pastry flour. That gives the raspberries some grip so that they don't sink so easy depending on the type of cake batter.

Wait a minute, I said something about an extended thaw period. Why that matters is the freezing and thawing can rupture cell walls within the raspberries(think bottle of water in freezer)and degrades quality. They're rapidly frozen to reduce the stress on the fruit minimizing damage. That process is expensive which is why the fruit is more expensive or the name brand. Thawing them slowly in the refrigerator also reduces stress and helps to keep them from turning to mush. Thaw them too quickly and they can turn to mush. Buying quality frozen fruit gives me a head start on presentation.