Surgical scalpels and Xacto blades are NOT the same - having worked with both I can promise you this. Scalpels are made from a finer grade steel that is much thinner than your standard Xacto blade. They make a cleaner cut, but they are really only meant to be used for one project then thrown away. Because they're thinner, they are more prone to breaking.
...when it comes to fragging, I don't think it matters. I'd use a scalpel for fragging softies if you had access, but if not a standard #11 is just fine.