[RedDevil]

Only thing I can think of is that you can keep turning the engine over for a long time when push starting it (like rolling down a hill).
If the engine does not ignite the fuel inevitably will build up in the cat.

The same happens if you try to start it with the key, but the battery will run out at some point and protect you from killing the cat.
Hook the non-firing engine's battery up to a running car's battery, keep key starting and you'd kill the cat just like that.

So, nothing to worry about as long as the engine does fire up, carbs or not.
As bump starting won't cause the voltage to drop like key starting does, chances are that it will even fire up easier and cleaner than by key.