Yes, rushing yards count on a fumble. No matter if the player has gained negative or positive rushing yards before the fumble, the yards gained or lost are added to that player's yardage totals.

What is the fumble rule?

When a player is in control of the ball and attempting to pass it forward, any intentional forward movement of his hand starts a forward pass. ... If the player loses possession after he has tucked the ball into his body, it is a fumble.

Do yards after catch count towards receiving yards?

Exactly. A pass that travels 8 yards, gets caught, and then the receiver is immediately tackled isn't as good as one that only goes 5 yards, but allows the receiver 4+ yards of running after the fact.