I will test it tomorrow.
RealCADD is not code signing and not sandboxing.
So there is probably two different situations if RealCADD is installed before Mountain Lion or after.
To install it after Mountain Lion, the user will have to change prefs in GateKeeper.
Apparently there is no problem with Mountain Lion and RealCADD 4.21b2.
The only think I found is, as I write before, if you have to install it on Mountain Lion.
Because RealCADD is not codesigned, you have an alert and you have to go in System prefs to accept all applications.