The tackle should be legal if you come in from the frount, cleats down, and hit the ball first. I alot of it depends on the refs though, some have given me fouls for perfect tackles and others let me off with tackle from behind, (an accident)
There are more experianced keepers playing, but even experiance can't teach the instinct that nut greet has. Imagine what he can be with a few years experiance under his belt!