The fact of the inverse square law of gravity demands that gravitational radiation be massless.
presumably they can't escape.
Light is massless, but still that can't escape from a black hole.
You need to think in terms of inertial frames. Event horizons, for example, exist between locations not because there is some physical barrier between them, but because the difference between the inertial frames exceeds the speed of light. Signals from one point to the other can't run fast enough to catch up. It's a question of point-of-view.
Gravitational waves are also a point-of-view thing. The Earth, for example, radiates gravitational waves into space as it whips around the sun. The planet Mars, for example, feels (however feebly) the changing gravitational field of the Earth as it wobbles back and forth in its orbit. We here on Earth, however, can't feel those waves. It doesn't make sense to talk about measuring them as they travel from the center of the Earth on their way to Mars, for the simple fact that the waves don't travel along any such path. From where we're sitting, the gravitational field of the Earth doesn't change at all; there are no such waves to measure, from our point-of-view.
Can you elaborate on how the field changes as the hole absorbs new mass?
I.E. suppose a star falls into the hole, increasing its mass greatly. You are orbiting the hole at a nice safe distance. Does your orbital speed change? (Does the observed gravitational field of the hole change?) If so, how is the change communicated to the outside world?
Presumably by gravity waves. Eventually the field 'settles down' to its new value.
If the source of the field (the new, stronger one) is the event horizon, then the hole cannot appear as a "point source" of gravity (a particle) since the source is distributed. I'm thinking of Lambert's cosine law for radiation.
In other words, I am still confused and need instruction!
--Boris