a) If you are willing to pay Apple for the developer program then you are free to run whatever applications you like on your phone. It's how many of us are running terminals, emulators etc.
b) Apple charges 15% for developers earning less than $1m a year.
I don't understand how even as low as 15% of all the apps revenue can be less than $1m a year though and, if it is, why would Apple even bother collecting it.
b) Apple charges 15% for developers earning less than $1m a year.