I'm no expert, but i think these answers are ok.
1. Once the black hole has formed, anything you throw in to try to
disperse it only makes it more massive. if it were not for quantum
fluctuations, that would be a one-way street. Ultimately, black holes
should evaporate via quantum effects on the event horizon, but the more
stuff you throw in, the longer that takes.
2. Yes, in the notation that Einstein used, mass and energy are
exactly the same thing, just measured in different units. However, the
rest mass part of that is somehwat special in that it exists regardless
of the momentum of the object, i.e. independent of whether the object
is moving in your favorite reference frame. In modern terminology,
sometimes that part is simply referred to as the 'mass'. In some
processes (e.g. radioactive decay) particles change to types with
different net rest mass, so there must be some other sort of energy
released, i.e. some type associated with the momentum of the particles.
The important question is 'which quantity is conserved," i.e.
which one doesn't change in time. That's the total mass-energy,
counting all the terms, including a gravitational potential term.
Usually we describe black holes in frames in which their velocity is
small compared to the speed of light, and so are the initial velocities
of the things that fall in, so you can get away with treating the black
hole mass as the sum of the masses of the things that fell in.
The stuff that falls into black holes usually picks up a lot of
speed as it drops in. Tidal forces tear the stuff apart, and it usually
swirls around a bit before in an accretion disk before falling in. In
the process, electrons can be stripped from atoms and accelerated along
powerful magnetic fields. Black holes are often X-ray sources for this
reason. The point here is that the gravitational potential energy of
stuff before it fell in gets added to the mass of the black hole as
well. It's probably a small fraction of the energy of the stuff falling
in given its rest mass.
(published on 10/22/2007)